Patterning process and resist composition

ABSTRACT

A pattern is formed by coating a first positive resist composition comprising a copolymer comprising lactone-containing recurring units, acid labile group-containing recurring units and carbamate-containing recurring units, and a photoacid generator onto a substrate to form a first resist film, patternwise exposure, PEB, and development to form a first resist pattern, heating the first resist pattern for inactivation to acid, coating a second positive resist composition comprising a C 3 -C 8  alcohol and an optional C 6 -C 12  ether onto the first resist pattern-bearing substrate to form a second resist film, patternwise exposure, PEB, and development to form a second resist pattern.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 12/849,344, filed Aug. 3, 2010, which is based upon thenon-provisional application and claims priority under 35 U.S.C. §119(a)on Patent Application No. 2009-181504 filed in Japan on Aug. 4, 2009,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a patterning process involving the steps offorming a first resist pattern from a first resist film through exposureand development, heating the first resist pattern to generate a base forinactivation to acid, coating a second positive resist compositioncomprising a solvent containing a C₃-C₈ alcohol and an optional C₆-C₁₂ether and not dissolving away the first resist pattern, and forming asecond resist pattern in a selected area of the first resist patternwhere no pattern features are formed, thereby reducing the distancebetween pattern features. It also relates to a resist composition usedin the process.

BACKGROUND ART

In the recent drive for higher integration and operating speeds in LSIdevices, the pattern rule is made drastically finer. Thephotolithography which is currently on widespread use in the art isapproaching the essential limit of resolution determined by thewavelength of a light source. As the light source used in thelithography for resist pattern formation, g-line (436 nm) or i-line (365nm) from a mercury lamp was widely used in 1980's. Reducing thewavelength of exposure light was believed effective as the means forfurther reducing the feature size. For the mass production process of 64MB dynamic random access memories (DRAM, processing feature size 0.25 μmor less) in 1990's and later ones, the exposure light source of i-line(365 nm) was replaced by a KrF excimer laser having a shorter wavelengthof 248 nm. However, for the fabrication of DRAM with a degree ofintegration of 256 MB and 1 GB or more requiring a finer patterningtechnology (processing feature size 0.2 μm or less), a shorterwavelength light source was required. Over a decade, photolithographyusing ArF excimer laser light (193 nm) has been under activeinvestigation. It was expected at the initial that the ArF lithographywould be applied to the fabrication of 180-nm node devices. However, theKrF excimer lithography survived to the mass-scale fabrication of 130-nmnode devices. So, the full application of ArF lithography started fromthe 90-nm node. The ArF lithography combined with a lens having anincreased numerical aperture (NA) of 0.9 is considered to comply with65-nm node devices. For the next 45-nm node devices which required anadvancement to reduce the wavelength of exposure light, the F₂lithography of 157 nm wavelength became a candidate. However, for thereasons that the projection lens uses a large amount of expensive CaF₂single crystal, the scanner thus becomes expensive, hard pellicles areintroduced due to the extremely low durability of soft pellicles, theoptical system must be accordingly altered, and the etch resistance ofresist is low; the postponement of F₂ lithography and the earlyintroduction of ArF immersion lithography were advocated (see Proc. SPIEVol. 4690 xxix, 2002).

In the ArF immersion lithography, the space between the projection lensand the wafer is filled with water. Since water has a refractive indexof 1.44 at 193 nm, pattern formation is possible even using a lenshaving a numerical aperture (NA) of 1.0 or greater. Theoretically, it ispossible to increase the NA to nearly 1.44. It was initially recognizedthat the resolution could be degraded and the focus be shifted by avariation of water's refractive index with a temperature change. Theproblem of refractive index variation could be solved by controlling thewater temperature within a tolerance of 1/100° C. while it wasrecognized that the impact of heat from the resist film upon lightexposure drew little concern. There was a likelihood that micro-bubblesin water could be transferred to the pattern. It was found that the riskof bubble generation is obviated by thorough deaeration of water and therisk of bubble generation from the resist film upon light exposure issubstantially nil. At the initial phase in 1980's of the immersionlithography, a method of immersing an overall stage in water wasproposed. Later proposed was a partial-fill method of using a waterfeed/drain nozzle for introducing water only between the projection lensand the wafer so as to comply with the operation of a high-speedscanner. In principle, the immersion technique using water enabled lensdesign to a NA of 1 or greater. In optical systems based on traditionalrefractive index materials, this leads to giant lenses, which woulddeform by their own weight. For the design of more compact lenses, acatadioptric system was proposed, accelerating the lens design to a NAof 1.0 or greater. A combination of a lens having NA of 1.2 or greaterwith strong resolution enhancement technology suggests a way to the45-nm node (see Proc. SPIE Vol. 5040, p 724, 2003). Efforts have alsobeen made to develop lenses of NA 1.35.

One candidate for the 32-nm node lithography is lithography usingextreme ultraviolet (EUV) radiation with wavelength 13.5 nm. The EUVlithography has many accumulative problems to be overcome, includingincreased laser output, increased sensitivity, increased resolution andminimized line edge or width roughness (LER or LWR) of resist film,defect-free MoSi laminate mask, reduced aberration of reflection mirror,and the like.

The water immersion lithography using a NA 1.35 lens achieves anultimate resolution of 40 to 38 nm at the maximum NA, but cannot reach32 nm. Efforts have been made to develop higher refractive indexmaterials in order to further increase NA. It is the minimum refractiveindex among projection lens, liquid, and resist film that determines theNA limit of lenses. In the case of water immersion, the refractive indexof water is the lowest in comparison with the projection lens(refractive index 1.5 for synthetic quartz) and the resist film(refractive index 1.7 for prior art methacrylate-based film). Thus theNA of projection lens is determined by the refractive index of water.Recent efforts succeeded in developing a highly transparent liquidhaving a refractive index of 1.65. In this situation, the refractiveindex of projection lens made of synthetic quartz is the lowest,suggesting a need to develop a projection lens material with a higherrefractive index. LuAG (lutetium aluminum garnet Lu₃Al₅O₁₂) having arefractive index of at least 2 is the most promising material, but hasthe problems of birefringence and noticeable absorption. Even if aprojection lens material with a refractive index of 1.8 or greater isdeveloped, the liquid with a refractive index of 1.65 limits the NA to1.55 at most, failing in resolution of 32 nm. For resolution of 32 nm, aliquid with a refractive index of 1.8 or greater is necessary. Such aliquid material has not been discovered because a tradeoff betweenabsorption and refractive index is recognized in the art. In the case ofalkane compounds, bridged cyclic compounds are preferred to linear onesin order to increase the refractive index, but the cyclic compoundsundesirably have too high a viscosity to follow high-speed scanning onthe exposure tool stage. If a liquid with a refractive index of 1.8 isdeveloped, then the component having the lowest refractive index is theresist film, suggesting a need to increase the refractive index of aresist film to 1.8 or higher.

The process that now draws attention under the above-discussedcircumstances is a double patterning process involving a first set ofexposure and development to form a first pattern and a second set ofexposure and development to form a pattern between features of the firstpattern. See Proc. SPIE Vol. 5992, 59921Q-1-16 (2005). A number ofdouble patterning processes are proposed. One exemplary process involvesa first set of exposure and development to form a photoresist patternhaving lines and spaces at intervals of 1:3, processing the underlyinglayer of hard mask by dry etching, applying another layer of hard maskthereon, a second set of exposure and development of a photoresist filmto form a line pattern in the spaces of the first exposure, andprocessing the hard mask by dry etching, thereby forming aline-and-space pattern at a half pitch of the first pattern. Analternative process involves a first set of exposure and development toform a photoresist pattern having spaces and lines at intervals of 1:3,processing the underlying layer of hard mask by dry etching, applying aphotoresist layer thereon, a second set of exposure and development toform a second space pattern on the remaining hard mask portion, andprocessing the hard mask by dry etching. In either process, the hardmask is processed by two dry etchings.

While the former process requires two applications of hard mask, thelatter process uses only one layer of hard mask, but requires to form atrench pattern which is difficult to resolve as compared with the linepattern. The latter process includes the use of a negative resistmaterial in forming the trench pattern. This allows for use of highcontrast light as in the formation of lines as a positive pattern.However, since the negative resist material has a lower dissolutioncontrast than the positive resist material, a comparison of theformation of lines from the positive resist material with the formationof a trench pattern of the same size from the negative resist materialreveals that the resolution achieved with the negative resist materialis lower. After a wide trench pattern is formed from the positive resistmaterial by the latter process, there may be applied a thermal flowmethod of heating the substrate for shrinkage of the trench pattern, ora RELACS method of coating a water-soluble film on the trench pattern asdeveloped and heating to induce crosslinking at the resist film surfacefor achieving shrinkage of the trench pattern. These have the drawbacksthat the proximity bias is degraded and the process is furthercomplicated, leading to reduced throughputs.

Both the former and latter processes require two etchings for substrateprocessing, leaving the issues of a reduced throughput and deformationand misregistration of the pattern by two etchings.

One method that proceeds with a single etching is by using a negativeresist material in a first exposure and a positive resist material in asecond exposure. Another method is by using a positive resist materialin a first exposure and a negative resist material in an alcohol thatdoes not dissolve away the positive resist material in a secondexposure. Since negative resist materials with low resolution are used,these methods entail degradation of resolution (see JP-A 2008-078220).

If first exposure is followed by second exposure at a half-pitch shiftedposition, the optical energy of second exposure offsets the opticalenergy of first exposure so that the contrast becomes zero. If acontrast enhancement layer (CEL) is formed on the resist film, theincident light to the resist film becomes nonlinear so that the firstand second exposures do not offset each other. Thus an image having ahalf pitch is formed. See Jpn. J. Appl. Phy. Vol. 33 (1994) p 6874-6877.It is expected that similar effects are produced by using an acidgenerator capable of two photon absorption to provide a nonlinearcontrast.

The critical issue associated with double patterning is an overlayaccuracy between first and second patterns. Since the magnitude ofmisregistration is reflected by a variation of line size, an attempt toform 32-nm lines at an accuracy of 10%, for example, requires an overlayaccuracy within 3.2 nm. Since currently available scanners have anoverlay accuracy of the order of 8 nm, a significant improvement inaccuracy is necessary.

Now under investigation is the resist pattern freezing technologyinvolving forming a first resist pattern on a substrate, taking anysuitable means for insolubilizing the resist pattern with respect to theresist solvent and alkaline developer, applying a second resist thereon,and forming a second resist pattern in space portions of the firstresist pattern. With this freezing technology, etching of the substrateis required only once, leading to improved throughputs and avoiding theproblem of misregistration due to stress relaxation of the hard maskduring etching.

With respect to the freezing technology, a number of reports have beenpublished. Known are thermal insolubilization (Proc. SPIE Vol. 6923, p69230G (2008)); coating of a cover film and thermal insolubilization(Proc. SPIE Vol. 6923, p 69230H (2008)); insolubilization by irradiationof light having an extremely short wavelength, for example, 172 nmwavelength (Proc. SPIE Vol. 6923, p 692321 (2008)); insolubilization byion implantation (Proc. SPIE Vol. 6923, p 692322 (2008));insolubilization through formation of thin-film oxide film by CVD;insolubilization by light irradiation and special gas treatment (Proc.SPIE Vol. 6923, p 69233C1 (2008)); insolubilization of a resist patternby treatment of resist pattern surface with a metal alkoxide or metalhalide (e.g., titanium, zirconium or aluminum) or anisocyanate-containing silane compound (JP-A 2008-033174);insolubilization of a resist pattern by coating its surface withwater-soluble resin (JP-A 2008-083537); insolubilization by ethylenediamine gas and baking (J. Photopolym. Sci. Technol., Vol. 21, No. 5, p655 (2008)); and insolubilization by coating of an amine-containingsolution and hard-baking for crosslinking (WO 2008/070060).

With respect to the freezing technology, one basic idea is proposed inWO 2008/059440. JP-A 2008-192774 discloses a method includinginsolubilizing a first resist pattern by application of radiation andheat, coating the insolubilized pattern with a resist solutioncomprising a base polymer comprising recurring units havinghexafluoroalcohol groups and acid labile groups in an alcohol solvent,and forming a second resist pattern therefrom. These insolubilizationmethods, which involve heat treatment at elevated temperature, give riseto problems of pattern deformation, especially film slimming, and sizenarrowing or widening, which must be overcome.

Also known in the art are nitrobenzyl carbamates as a photobasegenerator (J. Am. Chem. Soc. 1991, 113, p 4303-4313) and photoresistcompositions comprising the same (JP-A H07-134399 and Proc. SPIE Vol.1466, p 75 (1991)). Specifically, JP-A H07-134399 discloses a chemicallyamplified resist composition comprising a polymer having a base labilefunctional group and a photobase generator. In Proc. SPIE Vol. 1466, p75 (1991), a resist film is coated and then heated to decompose athermal acid generator to generate an acid and to generate a base in theexposed area for neutralizing the acid, and the portion where the acidis present is crosslinked to form a positive pattern. It is alsoproposed in JP-A H10-083079 to add a photobase generator to aconventional positive photoresist composition comprising a base polymerhaving acid labile groups and a photoacid generator. JP-A 2003-313464discloses an ink composition for UV inkjet printing comprising aphotoacid generator and a thermal base generator. JP-A 2007-056196discloses a composition comprising a polyimide precursor and a thermalbase generator wherein polyimide is formed by heating.

Base amplifiers capable of generating a basic substance under the actionof an amine are proposed in JP-A 2000-330270 and JP-A 2002-128750.Polymerizable monomers having a base amplifying function and polymersresulting therefrom are described in JP-A 2002-265531.

CITATION LIST

-   -   Patent Document 1: JP-A 2008-033174    -   Patent Document 2: JP-A 2008-083537    -   Patent Document 3: WO 2008/070060    -   Patent Document 4: WO 2008/059440    -   Patent Document 5: JP-A 2008-192774    -   Patent Document 6: JP-A 2008-078220    -   Patent Document 7: JP-A H07-134399    -   Patent Document 8: JP-A H10-083079    -   Patent Document 9: JP-A 2003-313464    -   Patent Document 10: JP-A 2007-056196    -   Patent Document 11: JP-A 2000-330270    -   Patent Document 12: JP-A 2002-128750    -   Patent Document 13: JP-A 2002-265531    -   Non-Patent Document 1: Proc. SPIE Vol. 4690, xxix, 2002    -   Non-Patent Document 2: Proc. SPIE Vol. 5040, p 724, 2003    -   Non-Patent Document 3: Proc. SPIE Vol. 5992, 59921Q-1-16, 2005    -   Non-Patent Document 4: Jpn. J. Appl. Phy., Vol. 33 (1994), p        6874-6877    -   Non-Patent Document 5: Proc. SPIE Vol. 6923, p 69230G (2008)    -   Non-Patent Document 6: Proc. SPIE Vol. 6923, p 69230H (2008)    -   Non-Patent Document 7: Proc. SPIE Vol. 6923, p 692321 (2008)    -   Non-Patent Document 8: Proc. SPIE Vol. 6923, p 692322 (2008)    -   Non-Patent Document 9: Proc. SPIE Vol. 6923, p 69233C1 (2008)    -   Non-Patent Document 10: J. Photopolym. Sci. Technol., Vol. 21,        No. 5, p 655 (2008)    -   Non-Patent Document 11: J. Am. Chem. Soc. 1991, 113, p 4303-4313    -   Non-Patent Document 12: Proc. SPIE Vol. 1466, p 75 (1991)

SUMMARY OF INVENTION

It is understood that when substrate processing is carried out by doubledry etchings using resist patterns fabricated by double exposures anddevelopments, the throughput is reduced to one half Also an issue ofpattern misregistration by dry etchings occurs.

The above-mentioned methods of insolubilizing a resist pattern utilizehigh temperature and light irradiation which cause the pattern to bedeformed due to shrinkage. Upon heating and irradiation, the resistpattern undesirably experiences a reduction in pattern height or linewidth and longitudinal shrinkage.

Therefore, an object of the invention is to provide a pattern formingprocess in order to enable a double patterning process of processing asubstrate by a single dry etching. Another object is to provide a resistcomposition for use in the pattern forming process.

The inventors have found that a pattern forming process comprisingcoating a first positive resist composition comprising a copolymercomprising recurring units having lactone as an adhesive group,recurring units having an acid labile group, and recurring units havinga carbamate structure, effecting first exposure and development to forma first resist pattern, baking the first resist pattern to generate anamine compound from the recurring units having a carbamate structure forinactivating the pattern to acid, coating a second positive resistcomposition comprising a solvent containing an alcohol of 3 to 8 carbonatoms and an optional ether of 6 to 12 carbon atoms onto the firstresist pattern, and effecting second exposure and development to form asecond resist pattern is advantageous in that the inactivation treatmentprevents intermixing between the first and second resist films and alsoprevents the first resist pattern from being dissolved in the seconddeveloper even when the acid is generated in the first resist patternupon second exposure.

In one aspect, the invention provides a process for forming a pattern,comprising the steps of:

coating a first positive resist composition comprising a copolymercomprising recurring units having lactone as an adhesive group,recurring units having an acid labile group, and recurring units havinga carbamate structure, and a photoacid generator onto a substrate toform a first resist film, exposing the first resist film to high-energyradiation, post-exposure baking, and developing the first resist filmwith a developer to form a first resist pattern,

heating the first resist pattern at 100 to 200° C. for 3 to 200 secondsfor inactivating the first resist pattern to acid,

coating a second positive resist composition comprising a solventcontaining an alcohol of 3 to 8 carbon atoms and an optional ether of 6to 12 carbon atoms onto the first resist pattern-bearing substrate toform a second resist film, exposing the second resist film tohigh-energy radiation, post-exposure baking, and developing the secondresist film with a developer to form a second resist pattern.

In a preferred embodiment, the recurring units having a carbamatestructure are represented by formula (a1) or (a2) in the followinggeneral formula (1):

wherein R¹ and R⁷ are hydrogen or methyl, R² and R⁸ are a single bond,methylene, ethylene, phenylene, phenylmethylene, phenylethylene,phenylpropylene, or —C(═O)—R¹²—, wherein R¹² is a straight, branched orcyclic C₁-C₁₀ alkylene, C₆-C₁₀ arylene, or C₂-C₁₂ alkenylene group, R³and R⁹ are hydrogen or a straight, branched or cyclic C₁-C₁₀ alkyl, orwhen R² and R⁸ are —C(═O)—R¹²—, R³ and R⁹ may bond with R¹² to form aring with the nitrogen atom to which they are attached, R⁴, R⁵ and R⁶are hydrogen or a straight, branched or cyclic C₁-C₁₀ alkyl, C₆-C₁₄aryl, or C₇-C₁₄ alkenyl group, which may contain a straight, branched orcyclic C₁-C₆ alkyl, nitro, halogen, cyano, trifluoromethyl, carbonyl,ester, lactone ring, carbonate, maleimide, amide, C₁-C₆ alkoxy, or sulfogroup, R⁴ and R⁵, R⁵ and R⁶, or R⁴ and R⁶ may bond together to form aring with the carbon atom to which they are attached, exclusive of thecase where all of R⁴, R⁵ and R⁶ are hydrogen or alkyl, R¹⁰ and R¹¹ are aC₆-C₁₄ aryl or C₇-C₁₄ aralkyl group, which may contain a straight,branched or cyclic C₁-C₆ alkyl, nitro, halogen, cyano, trifluoromethyl,C₁-C₆ alkoxy, or carbonyl group.

In a preferred embodiment, the first resist pattern includes spaceswhere no pattern features are formed, and the second resist pattern isformed in the spaces of the first resist pattern, thereby reducing thedistance between the first and second pattern features. In anotherpreferred embodiment, the second resist pattern is formed so as to crossthe first resist pattern. In a further preferred embodiment, the secondresist pattern is formed in an area where the first resist pattern isnot formed and in a different direction from the first resist pattern.

In a preferred embodiment, one or both of the exposure steps to form thefirst and second resist patterns are by immersion lithography usingwater.

In a preferred embodiment, the second positive resist compositioncomprises a base polymer having a 2,2,2-trifluoro-1-hydroxyethyl group.More preferably, the base polymer in the second positive resistcomposition comprises recurring units having a2,2,2-trifluoro-1-hydroxyethyl group, represented by the general formula(2):

wherein R²¹ is hydrogen or methyl, X is a single bond, —O— or —C(═O)—O—,u is 1 or 2, in the case of u=1, R²² is a straight, branched or cyclicC₁-C₁₀ alkylene group which may contain an ester group, ether group orfluorine atom, or R²² may bond with R²³ to form a ring with the carbonatom to which they are attached, and in the case of u=2, R²² is theforegoing alkylene group, with one carbon-bonded hydrogen atomeliminated, and R²³ is hydrogen, C₁-C₆ alkyl or trifluoromethyl, or R²³is C₁-C₆ alkylene when it bonds with R²².

In a more preferred embodiment, the base polymer in the second positiveresist composition is a copolymer comprising recurring units (b) havinga 2,2,2-trifluoro-1-hydroxyethyl group and recurring units (c) having anacid labile group, represented by the general formula (3):

wherein X, R²¹, R²², R²³, and u are as defined above, R²⁴ is hydrogen ormethyl, R²⁵ is an acid labile group, b and c are numbers in the range:0<b<1.0, 0<c<1.0, and 0<b+c≦1.0.

In a further preferred embodiment, the base polymer in the secondpositive resist composition is a copolymer comprising recurring units(b) having a 2,2,2-trifluoro-1-hydroxyethyl group, recurring units (c)having an acid labile group, and recurring units (d-1) having a phenol,carboxyphenyl, hydroxynaphthyl or carboxynaphthyl group, represented bythe general formula (4):

wherein X, R²¹, R²², R²³, R²⁴, R²⁵, and u are as defined above, R²⁶ ishydrogen or methyl, Y is a single bond, —C(═O)—O— or —C(═O)—NH—, R²⁷ isa single bond or a straight or branched C₁-C₆ alkylene group, Z ishydroxyl or carboxyl, t is 0 or 1, v is 1 or 2, b, c and d-1 are numbersin the range: 0<b<1.0, 0<c<1.0, 0<(d-1)<1.0, and 0<b+c+(d-1)≦1.0.

In a further preferred embodiment, the base polymer in the secondpositive resist composition is a copolymer comprising recurring units(b) having a 2,2,2-trifluoro-1-hydroxyethyl group, recurring units (c)having an acid labile group, and recurring units (d-2) derived fromhydroxyacenaphthylene or carboxyacenaphthylene, represented by thegeneral formula (5):

wherein X, R²¹, R²², R²³, R²⁴, R²⁵, and u are as defined above, Z ishydroxyl or carboxyl, w is 1 or 2, b, c and d-2 are numbers in therange: 0<b<1.0, 0<c<1.0, 0<(d-2)<1.0, and 0<b+c+(d-2)≦1.0.

In a preferred embodiment, the alcohol of 3 to 8 carbon atoms isselected from the group consisting of

n-propanol, isopropyl alcohol, 1-butyl alcohol,

2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol,

1-pentanol, 2-pentanol, 3-pentanol, tert-amyl alcohol,

neopentyl alcohol, 2-methyl-1-butanol, 3-methyl-1-butanol,

3-methyl-3-pentanol, cyclopentanol, 1-hexanol, 2-hexanol,

3-hexanol, 2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol,

3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,

2-methyl-1-pentanol, 2-methyl-2-pentanol,

2-methyl-3-pentanol, 3-methyl-1-pentanol,

3-methyl-2-pentanol, 3-methyl-3-pentanol,

4-methyl-1-pentanol, 4-methyl-2-pentanol,

4-methyl-3-pentanol, 1-heptanol, cyclohexanol, and octanol,

and mixtures of two or more of the foregoing.

In a preferred embodiment, the ether of 6 to 12 carbon atoms is selectedfrom the group consisting of

methyl cyclopentyl ether, methyl cyclohexyl ether,

diisopropyl ether, diisobutyl ether, diisopentyl ether,

di-n-pentyl ether, methyl cyclopentyl ether,

methyl cyclohexyl ether, di-n-butyl ether,

di-sec-butyl ether, di-sec-pentyl ether, di-tert-amyl ether,

di-n-hexyl ether, anisole, 2-methylanisole, 3-methylanisole,

4-methylanisole, 2,3-dimethylanisole, 2,4-dimethylanisole,

3,4-dimethylanisole, 2,5-dimethylanisole,

2,6-dimethylanisole, 3,5-dimethylanisole,

3,6-dimethylanisole, 2,3,4-trimethylanisole,

2,3,6-trimethylanisole, 2,4,6-trimethylanisole,

2,4,5,6-tetramethylanisole, 2-ethylanisole, 3-ethylanisole,

4-ethylanisole, 2-isopropylanisole, 3-isopropylanisole,

4-isopropylanisole, 4-propylanisole, 2-butylanisole,

3-butylanisole, 4-butylanisole, 2-tert-butylanisole,

3-tert-butylanisole, 4-tert-butylanisole, pentamethylanisole,

2-vinylanisole, 3-vinylanisole, 4-methoxystyrene,

ethyl phenyl ether, propyl phenyl ether, butyl phenyl ether,

ethyl 3,5-xylyl ether, ethyl 2,6-xylyl ether,

ethyl 2,4-xylyl ether, ethyl 3,4-xylyl ether,

ethyl 2,5-xylyl ether, methyl benzyl ether,

ethyl benzyl ether, isopropyl benzyl ether,

propyl benzyl ether, methyl phenethyl ether,

ethyl phenethyl ether, isopropyl phenethyl ether,

propyl phenethyl ether, butyl phenethyl ether,

vinyl phenyl ether, allyl phenyl ether, vinyl benzyl ether,

allyl benzyl ether, vinyl phenethyl ether,

allyl phenethyl ether, 4-ethylphenetole, and

tert-butyl phenyl ether, and mixtures of two or more of the foregoing.

In a further preferred embodiment, the solvent containing an alcohol of3 to 8 carbon atoms and an optional ether of 6 to 12 carbon atoms in thesecond positive resist composition does not dissolve away the firstresist pattern, allows components of the second resist composition to bedissolved therein, and is such that the first resist film experiences aslimming of not more than 10 nm when the solvent is dispensed on thefirst resist film for 30 seconds and then removed by spin drying andbaking at a temperature not higher than 130° C.

In another aspect, the invention provides a resist compositioncomprising a base resin, a photoacid generator, and an organic solvent,wherein the base resin is a copolymer comprising recurring units havinglactone as an adhesive group, recurring units having an acid labilegroup, and recurring units represented by formula (a1) or (a2) in thefollowing general formula (1):

wherein R¹ to R¹¹ are as defined above.

Advantageous Effects of Invention

The pattern forming process ensures that as a result of doublepatterning including two exposures, a second resist pattern can beformed in a space portion of a first resist pattern without deformationof the first resist pattern.

According to the invention, a pattern is formed by coating a firstpositive resist composition comprising a copolymer comprising recurringunits having lactone as an adhesive group, recurring units having anacid labile group, and recurring units having a carbamate structure ontoa substrate to form a first resist film, exposing the first resist filmto high-energy radiation, PEB, and developing the first resist film witha developer to form a first resist pattern, heating the first resistpattern to generate a base from the recurring units having a carbamatestructure for inactivating the pattern to acid, coating a secondpositive resist composition comprising a C₃-C₈ alcohol or a mixture of aC₃-C₈ alcohol and a C₆-C₁₂ ether as a solvent onto the first resistpattern-bearing substrate to form a second resist film, exposing thesecond resist film to high-energy radiation, PEB, and developing thesecond resist film with a developer to form a second resist pattern.When the second pattern is formed in an area of the first pattern wherefirst pattern features have not been formed, for example, this doublepatterning reduces the pitch between pattern features to one half. Thesubstrate can be processed by a single dry etching.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a double patterning processaccording one embodiment of the invention. FIG. 1A shows a laminate ofsubstrate, processable layer, hard mask and first resist film, FIG. 1Bshows the first resist film being exposed and developed, FIG. 1C showsthe first resist film being inactivated to acid, FIG. 1D shows a secondresist film being formed, exposed and developed, FIG. 1E shows the hardmask being etched, and FIG. 1F shows the processable layer being etched.

FIG. 2 is a schematic view of a double patterning process according oneembodiment of the invention. FIG. 2A shows a first pattern being formed,and FIG. 2B shows a second pattern being formed.

FIG. 3 is a schematic view of a double patterning process accordinganother embodiment of the invention. FIG. 3A shows a first pattern beingformed, and FIG. 3B shows a second pattern being formed.

FIG. 4 is a cross-sectional view of an exemplary prior art doublepatterning process. FIG. 4A shows a laminate of substrate, processablelayer, hard mask and resist film, FIG. 4B shows the resist film beingexposed and developed, FIG. 4C shows the hard mask being etched, FIG. 4Dshows a second resist film being formed, exposed and developed, and FIG.4E shows the processable layer being etched.

FIG. 5 is a cross-sectional view of another exemplary prior art doublepatterning process. FIG. 5A shows a laminate of substrate, processablelayer, 1st and 2nd hard masks and resist film, FIG. 5B shows the resistfilm being exposed and developed, FIG. 5C shows the 2nd hard mask beingetched, FIG. 5D shows, after removal of the first resist film, a secondresist film being formed, exposed and developed, FIG. 5E shows the 1sthard mask being etched, and FIG. 5F shows the processable layer beingetched.

FIG. 6 is a cross-sectional view of a further exemplary prior art doublepatterning process. FIG. 6A shows a laminate of substrate, processablelayer, hard mask and resist film, FIG. 6B shows the resist film beingexposed and developed, FIG. 6C shows the hard mask being etched, FIG. 6Dshows, after removal of the first resist film, a second resist filmbeing formed, exposed and developed, FIG. 6E shows the hard mask beingetched, and FIG. 6F shows the processable layer being etched.

FIG. 7 is a plan view of a resist pattern evaluated by double patterningtest I.

FIG. 8 is a plan view of a resist pattern evaluated by double patterningtest II.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The singular forms “a,” “an” and “the” include plural referents unlessthe context clearly dictates otherwise. “Optional” or “optionally” meansthat the subsequently described event or circumstances may or may notoccur, and that description includes instances where the event orcircumstance occurs and instances where it does not. As used herein, theterminology “(C_(x)-C_(y))”, as applied to a particular unit, such as,for example, a chemical compound or a chemical substituent group, meanshaving a carbon atom content of from “x” carbon atoms to “y” carbonatoms per such unit. As used herein, the term “film” is usedinterchangeably with “coating” or “layer.” The term “processable layer”is interchangeable with patternable layer and refers to a layer that canbe processed such as by etching to form a pattern therein.

The abbreviations and acronyms have the following meaning.

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure baking

TMAH: tetramethylammonium hydroxide

PGMEA: propylene glycol monomethyl ether acetate

In connection with the double patterning lithography involving doubleexposures and developments to form a half-pitch pattern, the inventorsmade efforts to develop a positive resist material which enables toprocess a substrate by a single dry etching and a patterning processusing the same.

The inventors have discovered that a double patterning process capableof reducing the pitch between pattern features to one half can bepracticed by coating a first positive resist composition on a substrate,forming a first resist pattern through exposure and development, heatingthe first resist pattern to generate a basic compound to neutralize theacid, coating a second positive resist composition comprising a solventwhich contains a C₃-C₈ alcohol or a mixture of a C₃-C₈ alcohol and aC₆-C₁₂ ether onto the first resist pattern-bearing substrate, andforming a second resist pattern through exposure and development whileretaining the first resist pattern. Then the substrate can be processedby a single dry etching. The present invention is predicated on thisdiscovery.

The first and second positive resist compositions are chemicallyamplified positive resist compositions each comprising a base polymerand a solvent. At least the first positive resist composition should notbe dissolvable in the solvent of the second positive resist composition.When the first positive resist composition comprises a base polymercontaining lactone as the main adhesive group, it is not dissolvable inalcohol and ether solvents. On the other hand, in order that the secondpositive resist composition be dissolvable in alcohol and ethersolvents, the presence of weakly acidic hydroxyl groups in the basepolymer of the second positive resist composition is essential. Theweakly acidic hydroxyl groups include hexafluoroalcohol groups astypified by 2,2,2-trifluoro-1-hydroxyethyl, phenol groups, and carboxylgroups. Although benzene rings cannot be used as the base polymer forresist material on account of their strong absorption at wavelength 193nm or can be copolymerized only in a limited amount, naphthalene ringscan be applied to the resist base polymer because the absorption peakwavelength is shifted toward the longer wavelength side.

Most methods of insolubilizing the first resist pattern which have beenproposed thus far rely on heat treatment to induce crosslinking reactionfor curing. The heat treatment to induce crosslinking reaction is oftenat high temperatures above 140° C. If heated at temperatures above theglass transition temperature, the pattern may flow or the pattern mayshrink due to deprotection of acid labile groups. Shrinkage of thepattern leads to a problem of reducing the line width, pattern height,and pattern length and a problem that an elbow pattern is deformed androunded at its corner. To minimize pattern deformation, a means forinsolubilizing the first resist pattern without resorting to heattreatment or at a sufficiently low temperature to cause no patterndeformation is desired.

Upon patternwise exposure of the second resist film to radiation, thefirst resist pattern is also exposed to radiation. If a solvent whichdoes not dissolve away the first resist pattern is used in the secondresist composition, this prevents intermixing with the first resistpattern or dissolution of the first resist pattern during coating of thesecond resist composition. However, since the acid is generated in thefirst resist pattern upon exposure of the second resist film, the firstresist pattern can be dissolved away during development of the secondresist film.

If an amine component is present in the first resist pattern and inexcess relative to the acid generated upon second exposure, itinactivates or neutralizes the acid generated upon second exposure,preventing the first resist pattern from being dissolved away duringdevelopment of the second resist film. Usually, an amine quencher isadded to photoresist material for the purposes of increasing contrastand inhibiting acid diffusion, but in a smaller amount than the acidgenerator. In order that amine be available in a larger amount than theamount of the acid formed by decomposition of the acid generator in thefirst resist pattern, it is contemplated to previously add a thermalbase generator to the first resist material so that an amine compoundmay be generated in the first resist pattern by heating after itsformation. If the amine compound is bound to the backbone of thepolymer, the acid neutralizing ability is enhanced because the aminedoes not volatilize. Then a polymer having a base generatorcopolymerized therewith is necessary as the base resin for resistmaterials.

The base generator used herein is ideally a compound having a doublebond for copolymerization which is photo-insensitive, non-basic initself, and decomposable to generate an amine by heating at 100 to 200°C. Although salts of amines with carboxylic acids and salts of amineswith sulfonic acids are photo-insensitive and function as a thermal basegenerator, they are inadequate in that they function as a quencher byion exchange with a fluorosulfonic acid generated in the resist filmupon exposure. The amine compound in the form of t-butylcarbamatedescribed in JP-A 2001-166476 is decomposed with an acid to form anamine compound. It is undesirable that an amine is produced during PEB,because the amine is lost at this stage. Methyl carbamate is so heatstable that its decomposition requires heat treatment at a hightemperature above 200° C. The heat treatment at a high temperature above200° C., however, causes thermal flow to the resist pattern or inducesshrinkage due to decomposition of acid labile groups. In contrast, basegenerators in the form of benzylcarbamate or benzoincarbamate aredesirably used for the object of the invention since their pyrolysistemperature is about 150° C. or lower. Potential generation of a base ata temperature below 100° C. is undesirable because this indicates thatan amine generates during pre-baking after spin coating, resulting inthe first photoresist being reduced in sensitivity. An amine amplifierwhich is catalyzed by an amine to generate another amine compound isdesirably used for the object of the invention. The amine amplifiers aredescribed in JP-A 2000-330270 and JP-A 2002-265531. For the object ofthe invention, benzylcarbamate or benzoincarbamate type base generatorshaving a polymerizable double bond must be copolymerized.

Accordingly, the first positive resist composition used herein forforming the first resist pattern comprises a copolymer comprisingrecurring units having a lactone adhesive group, recurring units havingan acid labile group, and recurring units having a carbamate structureas the base resin, and a photoacid generator.

Preferably the recurring units having a carbamate structure arerepresented by formula (a1) or (a2) in the following general formula(1).

Herein R¹ and R⁷ are hydrogen or methyl. R² and R⁸ are a single bond,methylene, ethylene, phenylene, phenylmethylene, phenylethylene,phenylpropylene, or —C(═O)—R¹²—, wherein R¹² is a straight, branched orcyclic C₁-C₁₀ alkylene, C₆-C₁₀ arylene, or C₂-C₁₂ alkenylene group. R³and R⁹ are hydrogen or a straight, branched or cyclic C₁-C₁₀ alkyl, orwhen R² and R⁸ are —C(═O)—R¹²—, R³ and R⁹ may bond with R¹² to form aring with the nitrogen atom to which they are attached, preferably anon-aromatic ring composed of 3 to 8 carbon atoms and one nitrogen atom.R⁴, R⁵ and R⁶ are hydrogen or a straight, branched or cyclic C₁-C₁₀alkyl, C₆-C₁₄ aryl, or C₇-C₁₄ alkenyl group, which may contain astraight, branched or cyclic C₁-C₆ alkyl, nitro, halogen, cyano,trifluoromethyl, carbonyl, ester, lactone ring, carbonate, maleimide,amide, C₁-C₆ alkoxy, or sulfo group, a pair of R⁴ and R⁵, R⁵ and R⁶, orR⁴ and R⁶ may bond together to form a ring with the carbon atom to whichthey are attached, specifically a non-aromatic or aromatic ring of 3 to10 carbon atoms. The case where all of R⁴, R⁵ and R⁶ are hydrogen oralkyl is excluded. R¹⁰ and R¹¹ are a C₆-C₁₄ aryl or C₇-C₁₄ aralkylgroup, which may contain a straight, branched or cyclic C₁-C₆ alkyl,nitro, halogen, cyano, trifluoromethyl, C₁-C₆ alkoxy, or carbonyl group.The subscripts a1 and a2 are numbers in the range: 0≦a1<1.0, 0≦a2<1.0,and 0<a1+a2<1.0.

Of the compounds of formula (1), the carbamate type base generatorhaving a polymerizable double bond generates an amine via adecomposition mechanism as illustrated by the following scheme (6), andthe benzoincarbamate type base generator generates an amine via adecomposition mechanism as illustrated by the following scheme (7).Decomposition yields carbon dioxide, a secondary or primary aminecompound bound to a polymer backbone, and another compound.

Herein R¹ to R⁹ are as defined above. R and R′ are hydrogen, a straight,branched or cyclic C₁-C₆ alkyl, nitro, halogen, cyano, trifluoromethyl,carbonyl group, or C₁-C₆ alkoxy group.

Shown below are examples of the monomers from which the carbamate typebase generators represented by recurring units (a1) in formula (1) arederived. Herein, R¹ to R⁶ are as defined above.

Shown below are examples of the monomers from which the benzoincarbamatetype base generators represented by recurring units (a2) in formula (1)are derived. Herein, R⁷ to R¹¹ are as defined above.

While o-nitrobenzylcarbamate and benzoincarbamate are known as aphotobase generator, they also function as a thermal base generator.Since the efficiency of base generation of o-nitrobenzylcarbamate orbenzoincarbamate upon light exposure is of the order of ½ to ¼ of theefficiency of acid generation of triphenylsulfonium onium salts uponlight exposure, the o-nitrobenzylcarbamate or benzoincarbamate basegenerator, when combined with the triphenylsulfonium onium saltphotoacid generator, is left for the most part undecomposed at the endof exposure, allowing the base to be generated by subsequent heating.

The first resist composition for forming the first resist patterncomprises as a base resin a polymer further comprising recurring units(b⁰) having lactone as an adhesive group and recurring units (c) havingan acid labile group, preferably represented by the formula (A), inaddition to the recurring units (a1) or (a2) defined above.

Herein R³¹ and R²⁴ are hydrogen or methyl, R^(A) is a monovalent organicgroup having lactone structure, R²⁵ is an acid labile group, b⁰ and care numbers in the range: 0<b⁰<1.0, 0<c<1.0, and 0<b⁰+c<1.0.

Examples of recurring units (b⁰) are the same as will be laterexemplified for the recurring units having lactone structure amongrecurring units (e). Recurring units (c) will be described later. Inaddition to the recurring units (b⁰) and (c), the base resin in thefirst resist composition may further comprise recurring units (e) freeof lactone structure to be described later.

The second resist composition is used to form a second resist patternthrough second coating, exposure and development steps. The secondpositive resist composition comprises a base resin and a solvent whichcontains an alcohol of 3 to 8 carbon atoms or a mixture of an alcohol of3 to 8 carbon atoms and an ether of 6 to 12 carbon atoms and which doesnot dissolve away the first resist pattern. The base polymer must bedissolved in this solvent. The polymer to be dissolvable in this solventshould preferably have a 2,2,2-trifluoro-1-hydroxyethyl group, orhydroxyl or carboxyl-bearing naphthyl group, and is typically acopolymer comprising at least recurring units having the general formula(8).

Herein R²¹, R²⁴ and R²⁶ are hydrogen or methyl. X is a single bond, —O—or —C(═O)—O—. The subscript u is 1 or 2. In the case of u=1, R²² is astraight, branched or cyclic C₁-C₁₀ alkylene group which may contain anester group, ether group or fluorine atom, or R²² may bond with R²³ toform a non-aromatic ring with the carbon atom to which they areattached. In the case of u=2, R²² is the foregoing alkylene group, withone carbon-bonded hydrogen atom eliminated. R²³ is hydrogen, C₁-C₆ alkylor trifluoromethyl, or R²³ is C₁-C₆ alkylene when it bonds with R²². R²⁵is an acid labile group. Y is a single bond, —C(═O)—O— or —C(═O)—NH—.R²⁷ is a single bond or a straight or branched C₁-C₆ alkylene group. Zis hydroxyl or carboxyl. The subscripts v and w each are 1 or 2, t is 0or 1, b, c, d-1 and d-2 are numbers in the range: 0<b<1.0, 0<c<1.0,0≦(d-1)<1.0, 0≦(d-2)<1.0, and 0<b+c+(d-1)+(d-2)≦1.0.

Monomers from which recurring units (b) are derived include thefollowing monomers wherein R²¹ is as defined above.

Monomers from which recurring units (d-1) and (d-2) are derived aregiven below wherein R²⁶ is as defined above. It is noted thathydroxyvinylnaphthalene copolymers are described in JP 3829913 andhydroxyacenaphthylene copolymers are described in JP 3796568.

As the monomers corresponding to recurring units (b), (d-1) and (d-2),those monomers wherein a hydroxyl group is substituted by an acetalgroup or a formyl, acetyl or pivaloyl group may be used inpolymerization. After polymerization, the acetal group can be convertedback to a hydroxy group by hydrolysis with an acid. The formyl, acetylor pivaloyl group can be converted back to a hydroxy group by alkalinehydrolysis.

The polymer which can be used as the base resin in the second resistcomposition comprises recurring units (c) having an acid labile group inaddition to the recurring units (b).

Herein R²⁴ is hydrogen or methyl, and R²⁵ is an acid labile group.

Monomers Mc from which recurring units (c) (included in the first andsecond resist compositions) are derived are given below wherein R²⁴ andR²⁵ are as defined above.

The acid labile group represented by R²⁵ may be selected from a varietyof such groups. The acid labile groups may be the same or differentbetween the first and second resist compositions and preferably includegroups of the following formulae (A-1) to (A-3).

In formula (A-1), R^(L30) is a tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in whicheach alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms, or a group of formula (A-3). Exemplary tertiary alkylgroups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-2-oxooxolan-5-yl. Letter a11 is an integer of 0 to 6.

In formula (A-2), R^(L31) and R^(L32) are hydrogen or straight, branchedor cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms. Exemplary alkyl groups include methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl,2-ethylhexyl, and n-octyl. R^(L33) is a monovalent hydrocarbon group of1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, which may containa heteroatom such as oxygen, examples of which include straight,branched or cyclic alkyl groups and substituted forms of such alkylgroups in which some hydrogen atoms are replaced by hydroxyl, alkoxy,oxo, amino, alkylamino or the like. Illustrative examples of thesubstituted alkyl groups are shown below.

A pair of R^(L31) and R^(L32), R^(L31) and R^(L33), or R^(L32) andR^(L33) may bond together to form a ring with the carbon and oxygenatoms to which they are attached. Each of R^(L31), R^(L32) and R^(L33)is a straight or branched alkylene group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms when they form a ring, while the ringpreferably has 3 to 10 carbon atoms, more preferably 4 to 10 carbonatoms.

Examples of the acid labile groups of formula (A-1) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl groups.

Also included are substituent groups having the formulae (A-1)-1 to(A-1)-10.

Herein R^(L37) is each independently a straight, branched or cyclicC₁-C₁₀ alkyl group or C₆-C₂₀ aryl group, R^(L38) is hydrogen or astraight, branched or cyclic C₁-C₁₀ alkyl group, R^(L39) is eachindependently a straight, branched or cyclic C₂-C₁₀ alkyl group orC₆-C₂₀ aryl group, and a11 is as defined above.

Of the acid labile groups of formula (A-2), the straight and branchedones are exemplified by the following groups having formulae (A-2)-1 to(A-2)-35.

Of the acid labile groups of formula (A-2), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Other examples of acid labile groups include those of the followingformula (A-2a) or (A-2b) while the polymer may be crosslinked within themolecule or between molecules with these acid labile groups.

Herein R^(L40) and R^(L41) each are hydrogen or a straight, branched orcyclic C₁-C₈ alkyl group, or R^(L40) and R^(L41), taken together, mayform a ring with the carbon atom to which they are attached, and R^(L40)and R^(L41) are straight or branched C₁-C₈ alkylene groups when theyform a ring. R^(L42) is a straight, branched or cyclic C₁-C₁₀ alkylenegroup. Each of b11 and d11 is 0 or an integer of 1 to 10, preferably 0or an integer of 1 to 5, and c11 is an integer of 1 to 7. “A” is a(c11+1)-valent aliphatic or alicyclic saturated hydrocarbon group,aromatic hydrocarbon group or heterocyclic group having 1 to 50 carbonatoms, which may be separated by a heteroatom or in which some of thehydrogen atoms attached to carbon atoms may be substituted by hydroxyl,carboxyl, carbonyl groups or fluorine atoms. “B” is —CO—O—, —NHCO—O— or—NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkyltriyl and alkyltetrayl groups,and C₆-C₃₀ arylene groups, which may contain a heteroatom or in whichsome of the hydrogen atoms attached to carbon atoms may be substitutedby hydroxyl, carboxyl, acyl groups or halogen atoms. The subscript c11is preferably an integer of 1 to 3.

The crosslinking acetal groups of formulae (A-2a) and (A-2b) areexemplified by the following formulae (A-2)-36 through (A-2)-43.

In formula (A-3), R^(L34), R^(L35) and R^(L36) each are a monovalenthydrocarbon group, typically a straight, branched or cyclic C₁-C₂₀ alkylgroup, which may contain a heteroatom such as oxygen, sulfur, nitrogenor fluorine. A pair of R^(L34) and R^(L35), R^(L34) and R^(L36), orR^(L35) and R^(L36) may bond together to form a C₃-C₂₀ alicyclic ringwith the carbon atom to which they are attached.

Exemplary tertiary alkyl groups of formula (A-3) include tert-butyl,triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl,1-ethylcyclopentyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, andtert-amyl.

Other exemplary tertiary alkyl groups include those of the followingformulae (A-3)-1 to (A-3)-18.

Herein R^(L43) is each independently a straight, branched or cyclicC₁-C₈ alkyl group or C₆-C₂₀ aryl group, typically phenyl, R^(L44) andR^(L46) each are hydrogen or a straight, branched or cyclic C₁-C₂₀ alkylgroup, and R^(L45) is a C₆-C₂₀ aryl group, typically phenyl.

The polymer may be crosslinked within the molecule or between moleculeswith groups having R^(L47) which is a di- or multi-valent alkylene orarylene group, as shown by the following formulae (A-3)-19 and (A-3)-20.

Herein R^(L43) is as defined above, R^(L47) is a straight, branched orcyclic C₁-C₂₀ alkylene group or arylene group, typically phenylene,which may contain a heteroatom such as oxygen, sulfur or nitrogen, ande1 is an integer of 1 to 3.

In formulae (A-1), (A-2), and (A-3), R^(L30), R^(L33), and R^(L36) alsostand for substituted or unsubstituted aryl groups such as phenyl,p-methylphenyl, p-ethylphenyl and alkoxy-substituted phenyl, typicallyp-methoxyphenyl, and aralkyl groups such as benzyl and phenethyl, whichmay contain an oxygen atom, or in which hydrogen atoms attached tocarbon atoms are replaced by hydroxyl groups, or in which two hydrogenatoms are replaced by an oxygen atom to form a carbonyl group, asexemplified by alkyl groups and oxoalkyl groups of the followingformulae.

Of recurring units having acid labile groups of formula (A-3), recurringunits of (meth)acrylate having an exo-form structure represented by theformula (A-3)-21 are preferred.

Herein, R²⁴ and c are as defined above; R^(c3) is a straight, branchedor cyclic C₁-C₈ alkyl group or an optionally substituted C₆-C₂₀ arylgroup; R^(c4) to R^(c9), R^(c12) and R^(c13) are each independentlyhydrogen or a monovalent C₁-C₁₅ hydrocarbon group which may contain aheteroatom; and R^(c10) and R^(c11) are hydrogen. Alternatively, a pairof R^(c4) and R^(c5), R^(c6) and R^(c8), R^(c6) and R^(c9), R^(c7) andR^(c9), R^(c7) and R^(c13), R^(c8) and R^(c12), R^(c10) and R^(c11), orR^(c11) and R^(c12), taken together, may form a ring, and in this case,each ring-forming R is a divalent C₁-C₁₅ hydrocarbon group which maycontain a heteroatom. Also, a pair of R^(c4) and R^(c13), R^(c10) andR^(c13), or R^(c6) and R^(c8) which are attached to vicinal carbon atomsmay bond together directly to form a double bond. The formula alsorepresents an enantiomer.

The ester form monomers from which recurring units having an exo-formstructure represented by formula (A-3)-21 are derived are described inU.S. Pat. No. 6,448,420 (JP-A 2000-327633). Illustrative non-limitingexamples of suitable monomers are given below.

Also included in the acid labile groups of formula (A-3) are acid labilegroups of (meth)acrylate having furandiyl, tetrahydrofurandiyl oroxanorbornanediyl as represented by the following formula (A-3)-22.

Herein, R²⁴ and c are as defined above; R^(c14) and R^(c15) are eachindependently a monovalent, straight, branched or cyclic C₁-C₁₀hydrocarbon group, or R^(c14) and R^(c15), taken together, may form analiphatic hydrocarbon ring with the carbon atom to which they areattached. R^(c16) is a divalent group selected from furandiyl,tetrahydrofurandiyl and oxanorbornanediyl. R^(c17) is hydrogen or amonovalent, straight, branched or cyclic C₁-C₁₀ hydrocarbon group whichmay contain a heteroatom.

Examples of the monomers from which the recurring units substituted withacid labile groups having furandiyl, tetrahydrofurandiyl andoxanorbornanediyl are derived are shown below. Note that Me is methyland Ac is acetyl.

While the polymer used in the second resist composition preferablyincludes recurring units (b), (c) (d-1), and (d-2) as shown in formula(8), it may have copolymerized therein recurring units (e) derived froma monomer having a hydroxy, lactone ring, carbonate, cyano, ether orester group. Examples of the monomers from which recurring units (e) arederived are given below.

In the base resin for the second resist composition, any of recurringunits (g1), (g2), and (g3) having a sulfonium salt as represented by thegeneral formula (9) may be further copolymerized.

Herein R²⁰⁰, R²⁴⁰, and R²⁸⁰ each are hydrogen or methyl. R²¹⁰ is asingle bond, phenylene, —O—R— or —C(═O)—Y—R— wherein Y is an oxygen atomor NH, and R is a straight, branched or cyclic C₁-C₆ alkylene group,phenylene group or alkenylene group, which may contain a carbonyl(—CO—), ester (—COO—), ether (—O—) or hydroxy radical. R²²⁰, R²³⁰, R²⁵⁰,R²⁶⁰, R²⁷⁰, R²⁹⁰, R³⁰⁰, and R³¹⁰ are each independently a straight,branched or cyclic C₁-C₁₂ alkyl group which may contain a carbonyl,ester or ether radical, or a C₆-C₁₂ aryl group, C₂-C₂₀ aralkyl group orthiophenyl group. Z¹ is a single bond, methylene, ethylene, phenylene,fluorinated phenylene, —O—R³²⁰—, or —C(═O)—Z²—R³²⁰— wherein Z² is anoxygen atom or NH, and R³²⁰ is a straight, branched or cyclic C₁-C₆alkylene group, phenylene group or alkenylene group, which may contain acarbonyl, ester, ether or hydroxy radical. M⁻ is a non-nucleophiliccounter ion. The subscripts g1, g2 and g3 are numbers in the range:0≦g1≦0.3, 0≦g2≦0.3, 0≦g3≦0.3, and 0≦g1+g2+g3≦0.3.

Examples of the non-nucleophilic counter ion represented by M⁻ includehalide ions such as chloride and bromide ions; fluoroalkylsulfonate ionssuch as triflate, 1,1,1-trifluoroethanesulfonate, andnonafluorobutanesulfonate; arylsulfonate ions such as tosylate,benzenesulfonate, 4-fluorobenzenesulfonate,1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such asmesylate and butanesulfonate; imidates such asbis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide, andbis(perfluorobutylsulfonyl)imide; and methidates such astris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide.

Other non-nucleophilic counter ions include sulfonates having fluorinesubstituted at α-position as represented by the general formulae (K-1)and (K-2).

In formula (K-1), R¹⁰² is hydrogen, or a straight, branched or cyclicC₁-C₃₀ alkyl or acyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀ aryl oraryloxy group, which may have an ether, ester, carbonyl radical orlactone ring. In formula (K-2), R¹⁰³ is hydrogen, or a straight,branched or cyclic C₁-C₂₀ alkyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀aryl group, which may have an ether, ester, carbonyl radical or lactonering.

As described above, the base polymer in the first resist compositionused in the first patterning stage should be insoluble in the solventconsisting of a C₃-C₈ alcohol and an optional C₆-C₁₂ ether. The polymershould contain lactone-containing adhesive groups in order that thepolymer be insoluble in the solvent. On the other hand, since recurringunits (b), (d-1), and (d-2) facilitate dissolution in the C₃-C₈ alcoholand C₆-C₁₂ ether, these units should not be incorporated into the basepolymer of the first resist composition, or if incorporated, shoulddesirably be limited to a copolymerization proportion of up to 20 mol %.

Specifically, the base polymer in the first resist composition used inthe first patterning stage should comprise recurring units (a1) or (a2)having a carbamate structure, recurring units (c) having an acid labilegroup, and recurring units (b⁰) having lactone, and may have furthercopolymerized therein recurring units (e) having a hydroxy, carbonate,cyano, ether or ester group.

The base polymer in the first resist composition used in the firstpatterning stage comprises recurring units (a1) and/or (a2), (b⁰), (c),and (e) in a copolymerization proportion: 0≦a1<1.0, 0≦a2<1.0,0<a1+a2<1.0, 0<b⁰<1.0, 0<c<1.0, 0≦e<1.0, and 0<a1+a2+b⁰+c+e≦1.0;preferably 0≦a1≦0.5, 0≦a2'0.5, 0.01≦a1+a2≦0.5, 0.1≦b⁰≦0.9, 0.1≦c≦0.8,0.05≦e≦0.9, and 0.15≦b⁰+c+e<1.0; more preferably 0.015≦a1≦0.4,0.015≦a2≦0.4, 0.015≦a1+a2≦0.4, 0.2≦b⁰≦0.8, 0.15≦c≦0.7, 0.1≦e≦0.85, and0.2≦b⁰+c+e≦1.0.

The base polymer in the second resist composition used in the secondpatterning stage comprises recurring units (b), (c), (d-1), and (d-2) ina copolymerization proportion: 0<b<1.0, 0<c<1.0, 0≦(d-1)<1.0,0≦(d-2)<1.0, 0<b+c+(d-1)+(d-2)≦1.0, and 0.1≦b+(d-1)+(d-2)≦0.9;preferably 0.1≦b≦0.9, 0.1≦c≦0.8, 0≦(d-1)+(d-2)≦0.5,0.3≦b+c+(d-1)+(d-2)≦1.0, and 0.15≦b+(d-1)+(d-2)≦0.85; more preferably0.2≦b≦0.8, 0.15≦c≦0.7, 0≦(d-1)≦0.4, 0≦(d-2)≦0.4,0.4≦b+c+(d-1)+(d-2)≦1.0, and 0.2≦b+(d-1)+(d-2)≦0.8. Notably e is0≦e<1.0, preferably 0≦e≦0.7, and more preferably 0≦e≦0.6, andb+c+(d-1)+(d-2)+e≦1.0.

The meaning of b+c+(d-1)+(d-2)+e=1 is that in a polymer comprisingrecurring units (b), (c), (d-1), (d-2), and (e), the sum of recurringunits (b), (c), (d-1), (d-2), and (e) is 100 mol % based on the totalamount of entire recurring units. The meaning of b+c+(d-1)+(d-2)+e<1 isthat the sum of recurring units (b), (c), (d-1), (d-2), and (e) is lessthan 100 mol % based on the total amount of entire recurring units,indicating the inclusion of other recurring units, for example, units(g1), (g2) or (g3). Where recurring units (g1), (g2) or (g3) areincorporated, their proportion is preferably 0≦g1+g2+g3≦0.2.

The following description applies to both the first and second resistcompositions.

The polymer serving as the base resin in the resist material used in thepattern forming process of the invention should preferably have a weightaverage molecular weight (Mw) in the range of 1,000 to 500,000, and morepreferably 2,000 to 30,000, as measured by GPC using polystyrenestandards. With too low a Mw, the efficiency of thermal crosslinking inthe resist material after development may become low. A polymer with toohigh a Mw may lose alkali solubility and give rise to a footingphenomenon after pattern formation.

If a polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that foreign matter isleft on the pattern or the pattern profile is degraded. The influencesof molecular weight and dispersity become stronger as the pattern rulebecomes finer. Therefore, the multi-component copolymer shouldpreferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially1.0 to 1.5, in order to provide a resist composition suitable formicropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ incompositional ratio, molecular weight or dispersity is acceptable. Ablend of a polymer comprising recurring units having a base generatorincorporated therein and an ordinary polymer free of a base generator isalso acceptable.

The polymer used herein may be synthesized by any desired method, forexample, by dissolving unsaturated bond-containing monomerscorresponding to the respective units in an organic solvent, adding aradical initiator thereto, and effecting heat polymerization. Examplesof the organic solvent which can be used for polymerization includetoluene, benzene, tetrahydrofuran, diethyl ether and dioxane. Examplesof the polymerization initiator used herein include2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethyl-valeronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours. The acid labile group that has been incorporated in the monomermay be kept as such, or the acid labile group may be once removed withan acid catalyst and thereafter protected or partially protected.

The polymer is not limited to one type and a mixture of two or morepolymers may be added. The use of plural polymers allows for adjustmentof resist properties.

The first or second positive resist composition used herein may includean acid generator in order for the composition to function as achemically amplified positive resist composition. Typical of the acidgenerator used herein is a photoacid generator (PAG) capable ofgenerating an acid in response to actinic light or radiation. It is anycompound capable of generating an acid upon exposure to high-energyradiation. Suitable photoacid generators include sulfonium salts,iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, andoxime-O-sulfonate acid generators. The acid generators may be used aloneor in admixture of two or more. Exemplary acid generators are describedin U.S. Pat. No. 7,537,880 (JP-A 2008-111103, paragraphs [0122] to[0142]). The acid generator is typically used in an amount of 0.1 to 30parts, and preferably 0.5 to 25 parts by weight per 100 parts by weightof the base polymer.

The resist composition may further comprise an organic solvent, basiccompound, dissolution regulator, surfactant, and acetylene alcohol,alone or in combination.

Examples of the organic solvent added to the first resist compositionare described in U.S. Pat. No. 7,537,880 or JP-A 2008-111103, paragraphs[0144] to [0145]. The organic solvent used in the first resistcomposition may be any organic solvent in which the base resin, acidgenerator, and other components are soluble. Illustrative, non-limiting,examples of the organic solvent include ketones such as cyclohexanoneand methyl-2-n-amyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; esters such as PGMEA, propylene glycolmonoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate,methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butylacetate, tert-butyl propionate, and propylene glycol mono-tert-butylether acetate; and lactones such as y-butyrolactone. These solvents maybe used alone or in combinations of two or more thereof. Of the aboveorganic solvents, it is recommended to use diethylene glycol dimethylether, 1-ethoxy-2-propanol, PGMEA, and mixtures thereof because the acidgenerator is most soluble therein. An appropriate amount of the organicsolvent used is 200 to 8,000 parts, especially 400 to 6,000 parts byweight per 100 parts by weight of the base polymer.

In the second resist composition, the organic solvent comprises a C₃-C₈alcohol and optionally a C₆-C₁₂ ether. Examples of C₃-C₈ alcohol includen-propanol, isopropyl alcohol, 1-butyl alcohol, 2-butyl alcohol,isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol,3-pentanol, tert-amyl alcohol, neopentyl alcohol, 2-methyl-1-butanol,3-methyl-1-butanol, 3-methyl-3-pentanol, cyclopentanol, 1-hexanol,2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol,3,3-dimethyl-2-butanol, 2-ethyl-1-butanol, 2-methyl-1-pentanol,2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-1-pentanol,3-methyl-2-pentanol, 3-methyl-3-pentanol, 4-methyl-1-pentanol,4-methyl-2-pentanol, 4-methyl-3-pentanol, 1-heptanol, cyclohexanol, andoctanol.

Of the C₃-C₈ alcohols, preferred are primary C₄-C₈ alcohols including1-butyl alcohol, isobutyl alcohol, 1-pentanol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol,3,3-dimethyl-1-butanol, 2,2-diethyl-1-butanol, 2-methyl-1-pentanol,3-methyl-1-pentanol, 4-methyl-1-pentanol, 1-heptanol, and 1-octanol. Thefirst pattern resist is least soluble in the C₄-C₈ alcohols whereas thefluoroalcohol-containing polymer for the second resist is highly solublein primary alcohols.

Examples of the C₆-C₁₂ ether include methyl cyclopentyl ether, methylcyclohexyl ether, diisopropyl ether, diisobutyl ether, diisopentylether, di-n-pentyl ether, methyl cyclopentyl ether, methyl cyclohexylether, di-n-butyl ether, di-sec-butyl ether, di-sec-pentyl ether,di-tert-amyl ether, di-n-hexyl ether, anisole, 2-methylanisole,3-methylanisole, 4-methylanisole, 2,3-dimethylanisole,2,4-dimethylanisole, 3,4-dimethylanisole, 2,5-dimethylanisole,2,6-dimethylanisole, 3,5-dimethylanisole, 3,6-dimethylanisole,2,3,4-trimethylanisole, 2,3,6-trimethylanisole, 2,4,6-trimethylanisole,2,4,5,6-tetramethylanisole, 2-ethylanisole, 3-ethylanisole,4-ethylanisole, 2-isopropylanisole, 3-isopropylanisole,4-isopropylanisole, 4-propylanisole, 2-butylanisole, 3-butylanisole,4-butylanisole, 2-tert-butylanisole, 3-tert-butylanisole,4-tert-butylanisole, pentamethylanisole, 2-vinylanisole, 3-vinylanisole,4-methoxystyrene, ethyl phenyl ether, propyl phenyl ether, butyl phenylether, ethyl 3,5-xylyl ether, ethyl 2,6-xylyl ether, ethyl 2,4-xylylether, ethyl 3,4-xylyl ether, ethyl 2,5-xylyl ether, methyl benzylether, ethyl benzyl ether, isopropyl benzyl ether, propyl benzyl ether,methyl phenethyl ether, ethyl phenethyl ether, isopropyl phenethylether, propyl phenethyl ether, butyl phenethyl ether, vinyl phenylether, allyl phenyl ether, vinyl benzyl ether, allyl benzyl ether, vinylphenethyl ether, allyl phenethyl ether, 4-ethylphenetole, and tert-butylphenyl ether, and mixtures of two or more of the foregoing.

Of the C₆-C₁₂ ethers, preferred are C₈-C₁₂ ethers including diisobutylether, diisopentyl ether, di-n-pentyl ether, di-n-butyl ether,di-sec-butyl ether, di-sec-pentyl ether, di-tert-amyl ether, di-n-hexylether, 2-methylanisole, 3-methylanisole, 4-methylanisole,2,3-dimethylanisole, 2,4-dimethylanisole, 3,4-dimethylanisole,2,5-dimethylanisole, 2,6-dimethylanisole, 3,5-dimethylanisole,3,6-dimethylanisole, 2,3,4-trimethylanisole, 2,3,6-trimethylanisole,2,4,6-trimethylanisole, 2,4,5,6-tetramethylanisole, 2-ethylanisole,3-ethylanisole, 4-ethylanisole, 2-isopropylanisole, 3-isopropylanisole,4-isopropylanisole, 4-propylanisole, 2-butylanisole, 3-butylanisole,4-butylanisole, 2-tert-butylanisole, 3-tert-butylanisole,4-tert-butylanisole, pentamethylanisole, 2-vinylanisole, 3-vinylanisole,4-methoxystyrene, ethyl phenyl ether, propyl phenyl ether, butyl phenylether, ethyl 3,5-xylyl ether, ethyl 2,6-xylyl ether, ethyl 2,4-xylylether, ethyl 3,4-xylyl ether, ethyl 2,5-xylyl ether, methyl benzylether, ethyl benzyl ether, isopropyl benzyl ether, propyl benzyl ether,methyl phenethyl ether, ethyl phenethyl ether, isopropyl phenethylether, propyl phenethyl ether, butyl phenethyl ether, vinyl phenylether, allyl phenyl ether, vinyl benzyl ether, allyl benzyl ether, vinylphenethyl ether, allyl phenethyl ether, 4-ethylphenetole, and tert-butylphenyl ether.

The C₈-C₁₂ ethers are characterized by a substantial insolubility of thefirst pattern therein. The polymer for use in the second resistcomposition does not dissolve in a C₈-C₁₂ ether when used alone, butdissolves in a mixture of a C₈-C₁₂ ether and a C₃-C₈ alcohol. Sincealcohols generally have a high viscosity, a photoresist compositioncontaining a polymer in an alcohol solvent is less amenable to spincoating. On the other hand, ethers have a low viscosity. Then a solventmixture of alcohol and ether is effective in reducing the viscosity ofthe resist composition, thereby facilitating the coating operationthereof. Of the alcohols used in the second resist composition, isobutylalcohol, 2-methyl-1-butanol and 3-methyl-1-butanol exhibit a highsolubility, but have a low boiling point and hence, a high evaporationrate during spin coating. In one version of the immersion lithographywherein a topcoat resist film is used in the absence of a protectivefilm, it is a common practice to add a polymeric substance capable ofimproving water repellency to the resist composition. During filmformation by spin coating, the water repellent substance segregates atthe resist surface. If the solvent has a low boiling point, the resistfilm will solidify before sufficient segregation of the water repellentsubstance occurs, resulting in only a slight improvement in waterrepellency. This problem is solved by blending a solvent having a highsolubility and a low boiling point with a solvent having a high boilingpoint. The high boiling solvents used are primary C₆-C₈ alcohols andC₈-C₁₂ ethers.

The solvent consisting of a C₃-C₈ alcohol or a C₃-C₈ alcohol and aC₆-C₁₂ ether should not dissolve away the first resist pattern, whereascomponents of the second resist composition should be dissolvabletherein. The standard by which the solvent consisting of a C₃-C₈ alcoholor a C₃-C₈ alcohol and a C₆-C₁₂ ether is judged as not dissolving awaythe first resist pattern is that the first resist film experiences aslimming of not more than 10 nm when the solvent is dispensed on thefirst resist film for 30 seconds and then removed by spin drying andbaking at a temperature not higher than 130° C.

Of various components for use in the first and second resistcompositions, exemplary basic compounds are described in JP-A2008-111103 (U.S. Pat. No. 7,537,880), paragraphs [0146] to [0164],including primary, secondary, and tertiary aliphatic amines, mixedamines, aromatic amines, heterocyclic amines, nitrogen-containingcompounds with carboxyl group, nitrogen-containing compounds withsulfonyl group, nitrogen-containing compounds with hydroxyl group,nitrogen-containing compounds with hydroxyphenyl group, alcoholicnitrogen-containing compounds, amides, imides, and carbamates. Exemplarysurfactants are described in JP-A 2008-111103, paragraphs [0165] to[0166]. Exemplary dissolution regulators are described in JP-A2008-122932 (US 2008090172), paragraphs [0155] to [0178], and exemplaryacetylene alcohols in paragraphs [0179] to [0182].

While the invention provides a pattern forming process using a resistcomposition based on a polymer having copolymerized therein recurringunits having a base generating mechanism, a base generator may be addedto the resist composition. The base generator typically includes thecompounds having the general formulae (10) to (15).

Herein R⁵¹, R⁵², R⁵³, R⁵⁶, R⁵⁷, R⁵⁸, R⁶², R⁶³, R⁶⁴, R⁶⁵, R⁶⁶, R⁶⁷, R⁷⁰,R⁷¹, R⁷², R⁷⁶, R⁷⁷ and R⁷⁸ are each independently hydrogen, a straight,branched or cyclic C₁-C₆ alkyl group, or a C₆-C₁₄ aryl group, which maybe substituted with a straight, branched or cyclic C₁-C₆ alkyl or alkoxygroup, nitro, halogen, cyano or trifluoromethyl group, at least one ofR⁵¹ to R⁵³, R⁵⁶ to R⁵⁸, R⁶² to R⁶⁴, R⁶⁵ to R⁶⁷, R⁷⁰ to R⁷², and R⁷⁶ toR⁷⁸ is an aryl or alkenyl group, and at least one is hydrogen, or atleast two of R⁵¹ to R⁵³, R⁵⁶ to R⁵⁸, R⁶² to R⁶⁴, R⁶⁵ to R⁶⁷, R⁷⁰ to R⁷²,and R⁷⁶ to R⁷⁸ may bond together to form a non-aromatic ring with thecarbon atom to which they are attached. R⁵⁴, R⁵⁵, R⁵⁹, R⁶¹, R⁶⁸, R⁶⁹,R⁷³, R⁷⁵, R⁸¹, R⁸², R⁸⁵, and R⁸⁷ are each independently hydrogen or astraight, branched or cyclic C₁-C₁₂ alkyl group which may contain adouble bond, ether, amino, carbonyl, hydroxyl or ester group, or a pairof R⁵⁴ and R⁵⁵, R⁵⁹ and R⁶¹, R⁵⁹ and R⁶⁰, R⁶¹ and R⁶⁰, R⁶⁸ and R⁶⁹, R⁷³and R⁷⁴, R⁷⁴ and R⁷⁵, R⁷³ and R⁷⁵, R⁸¹ and R⁸², R⁸⁵ and R⁸⁶, R⁸⁵ andR⁸⁷, and R⁸⁶ and R⁸⁷ may bond together to form a ring with the nitrogenatom or atoms to which they are attached. R⁶⁰, R⁷⁴ and R⁸⁶ are a singlebond, a straight, branched or cyclic C₁-C₂₀ alkylene or alkyne group,C₆-C₂₀ arylene, C₂-C₁₂ alkenylene, or C₂-C₁₂ alkynylene group, which maycontain a double bond, ether, amino, carbonyl, hydroxyl or ester group.R⁷⁹, R⁸⁰, R⁸³, R⁸⁴, R⁸⁸, and R⁸⁹ are a straight or branched C₁-C₆ alkylgroup, or a pair of R⁷⁹ and R⁸⁰, R⁸³ and R⁸⁴, and R⁸⁸ and R⁸⁹ may bondtogether to form a ring with the carbon and nitrogen atoms to which theyare attached, the ring optionally containing a benzene ring, naphthalenering, double bond or ether bond. The subscripts m, n, and r are 1 or 2.

The use of the base generator of any one of formulae (10) to (15)affords an amine propagating mechanism that an amine is generated fromthe compound comprising recurring units of formula (1) by utilizing as acatalyst an amine compound generated by the base generator of any one offormulae (10) to (15). This mechanism has the advantage of moreefficient amine generation.

Process

Now, the double patterning process is described. FIGS. 4 to 6 illustrateprior art double patterning processes.

Referring to FIG. 4, one exemplary double patterning process I isillustrated. A photoresist film 30 is coated and formed on a processablelayer 20 on a substrate 10. To prevent the photoresist pattern fromcollapsing, the technology intends to reduce the thickness ofphotoresist film. One approach taken to compensate for a lowering ofetch resistance of thinner film is to process the processable layerusing a hard mask. The double patterning process illustrated in FIG. 4uses a multilayer coating in which a hard mask 40 is laid between thephotoresist film 30 and the processable layer 20 as shown in FIG. 4A. Inthe double patterning process, the hard mask is not always necessary,and an underlayer film in the form of a carbon film and asilicon-containing intermediate film may be laid instead of the hardmask, or an organic antireflective coating may be laid between the hardmask and the photoresist film. The hard mask used herein may be of SiO₂,SiN, SiON, p-Si or TiN, for example. The resist material used in doublepatterning process I is a positive resist composition. In the process,the resist film 30 is exposed and developed (FIG. 4B), the hard mask 40is then dry etched (FIG. 4C), the photoresist film is stripped, and asecond photoresist film 50 is coated, formed, exposed, and developed(FIG. 4D). Then the processable layer 20 is dry etched (FIG. 4E). Sincethis etching is performed using the hard mask pattern and the secondphotoresist pattern as a mask, variations occur in the pattern sizeafter etching of the processable layer due to a difference in etchresistance between hard mask 40 and photoresist film 50.

To solve the above problem, a double patterning process II illustratedin FIG. 5 involves laying two layers of hard mask 41 and 42. The upperlayer of hard mask 42 is processed using a first resist pattern, thelower layer of hard mask 41 is processed using a second resist pattern,and the processable layer is dry etched using the two hard maskpatterns. It is essential to establish a high etching selectivitybetween first hard mask 41 and second hard mask 42. Thus the process israther complex.

FIG. 6 illustrates a double patterning process III using a trenchpattern. This process requires only one layer of hard mask. However,since the trench pattern is lower in optical contrast than the linepattern, the process has the drawbacks of difficult resolution of thepattern after development and a narrow margin. It is possible to form awide trench pattern and induce shrinkage by the thermal flow or RELACSmethod, but this process is more intricate. Using negative resistmaterials enables exposure at a high optical contrast, but the negativeresist materials generally have the drawbacks of low contrast and lowresolution capability as compared with positive resist materials. Thetrench process requires a very high accuracy of alignment because anymisalignment between the first and second trenches leads to a variationin the width of the finally remaining lines.

The double patterning processes I to III described above have thedrawback that two hard mask etchings are involved.

FIG. 1 illustrates the double patterning process of the invention. FIG.1A shows a structure wherein a first resist film 30 of the first resistcomposition is formed on a processable layer 20 on a substrate 10 via ahard mask 40 as in FIG. 4A. The first resist film 30 is exposedpatternwise and developed to form a first resist pattern (FIG. 1B). Thefirst resist film 30 is then baked whereby the base generator moiety isdecomposed to generate a base for thereby inactivating the first resistfilm 30 to acid, yielding an inactivated resist pattern 30 a (FIG. 1C).The preferred baking is at 100 to 200° C. for 3 to 200 seconds. Atemperature higher than 200° C. is undesired because the resist patternmay be deformed due to thermal flow or shrunk as a result ofdeprotection of acid labile groups. At temperatures below 100° C., thebase generator moiety is little decomposed. The heating or bakingtemperature is preferably 100° C. to 180° C., more preferably 110° C. to160° C., and even more preferably 110° C. to 150° C. The pattern islittle deformed if baking is at or below 150° C.

Next, the second resist composition is coated on the substrate to form asecond resist film. Through patternwise exposure and development of thesecond resist film, a second resist pattern 50 is formed in an areawhere features of the first resist film 30 (inactivated first resistpattern 30 a) have not been formed (FIG. 1D). Thereafter, the hard mask40 is etched (FIG. 1E). The processable layer 20 is dry etched, andfinally, the inactivated first resist pattern 30 a and second resistpattern 50 are removed (FIG. 1F).

Although the process illustrated in FIG. 1 forms the second patternbetween lines of the first pattern, it is also acceptable to form thesecond pattern so as to cross the first pattern orthogonally as shown inFIG. 2. Although such a pattern may be formed through a single exposurestep, an orthogonal line pattern may be formed at a very high contrastby a combination of dipolar illumination with polarized illumination.Specifically, pattern lines in Y-direction are formed as shown in FIG.2A and then protected from dissolution by the process of the invention.Thereafter, a second resist is coated and processed to form patternlines in X-direction as shown in FIG. 2B. Combining X and Y linesdefines a lattice-like pattern while empty areas become holes. Thepattern that can be formed by such a process is not limited to theorthogonal pattern, and may include a T-shaped pattern (not shown) or aseparated pattern as shown in FIG. 3B.

The substrate 10 used herein is generally a silicon substrate. Theprocessable layer 20 used herein includes SiO₂, SiN, SiON, SiOC, p-Si,a-Si, TiN, WSi, BPSG, SOG, Cr, CrO, CrON, MoSi, low dielectric film, andetch stopper film. The hard mask 40 is as described above.Understandably, an undercoat film in the form of a carbon film and anintermediate intervening layer in the form of a silicon-containingintermediate film or organic antireflective coating may be formedinstead of the hard mask.

In the process of the invention, a first resist film of a first positiveresist composition is formed on the processable layer directly or via anintermediate intervening layer such as the hard mask. The first resistfilm preferably has a thickness of 10 to 1,000 nm, and more preferably20 to 500 nm. The first resist film is heated or pre-baked prior toexposure, with the preferred pre-baking conditions including atemperature of 60 to 180° C., especially 70 to 150° C. and a time of 10to 300 seconds, especially 15 to 200 seconds.

This is followed by patternwise exposure. For the exposure, preferenceis given to high-energy radiation having a wavelength of 140 to 250 nm,and especially ArF excimer laser radiation of 193 nm. The exposure maybe done either in a dry atmosphere such as air or nitrogen stream, or byimmersion lithography in water. The ArF immersion lithography usesdeionized water or liquids having a refractive index of at least 1 andhighly transparent to the exposure wavelength such as alkanes as theimmersion solvent. The immersion lithography involves prebaking a resistfilm and exposing the resist film to light through a projection lens,with deionized water or another liquid introduced between the resistfilm and the projection lens. Since this allows lenses to be designed toa NA of 1.0 or higher, formation of finer feature size patterns ispossible. The immersion lithography is important for the ArF lithographyto survive to the 45-nm node. In the case of immersion lithography,deionized water rinsing (or post-soaking) may be carried out afterexposure for removing water droplets left on the resist film, or aprotective coating may be applied onto the resist film after pre-bakingfor preventing any leach-outs from the resist film and improving waterslip on the film surface. The resist protective coating used in theimmersion lithography is preferably formed from a solution of a polymerhaving 1,1,1,3,3,3-hexafluoro-2-propanol residues which is insoluble inwater, but soluble in an alkaline developer liquid, in a solventselected from alcohols of at least 4 carbon atoms, ethers of 8 to 12carbon atoms, and mixtures thereof. After formation of the photoresistfilm, deionized water rinsing (or post-soaking) may be carried out forextracting the acid generator and the like from the film surface orwashing away particles, or after exposure, rinsing (or post-soaking) maybe carried out for removing water droplets left on the resist film.

To the first resist composition, an additive for rendering the resistsurface water repellent may be added. A typical additive is a polymerhaving a fluoroalcohol group. After spin coating, the polymer segregatestoward the resist surface to reduce the surface energy, therebyimproving water slip. Such additives are described in JP-A 2007-297590and JP-A 2008-122932.

Exposure is preferably carried out so as to provide an exposure dose ofabout 1 to 200 mJ/cm², more preferably about 10 to 100 mJ/cm². This isfollowed by baking on a hot plate at 60 to 150° C. for 1 to 5 minutes,preferably at 80 to 120° C. for 1 to 3 minutes (post-exposurebaking=PEB).

Thereafter the resist film is developed with a developer in the form ofan aqueous alkaline solution, for example, an aqueous solution of 0.1 to5 wt %, preferably 2 to 3 wt % TMAH for 0.1 to 3 minutes, preferably 0.5to 2 minutes by conventional techniques such as dip, puddle or spraytechniques. In this way, a desired resist pattern is formed on thesubstrate.

With respect to the second resist pattern, the second resist compositionis coated, exposed and developed in a standard way. In one preferredembodiment, the second resist pattern is formed in an area wherefeatures of the first resist pattern have not been formed, therebyreducing the distance between pattern features to one half. Theconditions of exposure and development and the thickness of the secondresist film may be the same as described above.

Next, using the inactivated first resist film and the second resist filmas a mask, the intermediate intervening layer of hard mask or the likeis etched, and the processable layer further etched. For etching of theintermediate intervening layer of hard mask or the like, dry etchingwith fluorocarbon or halogen gases may be used. For etching of theprocessable layer, the etching gas and conditions may be properly chosenso as to establish an etching selectivity relative to the hard mask, andspecifically, dry etching with fluorocarbon, halogen, oxygen, hydrogenor similar gases may be used. Thereafter, the first and second resistfilms are removed. Removal of these films may be carried out afteretching of the intermediate intervening layer of hard mask or the like.It is noted that removal of the first resist film may be achieved by dryetching with oxygen or radicals, and removal of the second resist filmmay be achieved as previously described, or using strippers such asamines, sulfuric acid/aqueous hydrogen peroxide or organic solvents.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. For all polymers, Mw and Mn are determined by GPCversus polystyrene standards.

Synthesis Examples

Polymers to be added to resist compositions were prepared by combiningvarious monomers, effecting copolymerization reaction in tetrahydrofuranmedium, crystallization in methanol, repeatedly washing with hexane,isolation, and drying. The resulting polymers (Polymers 1-1 to 1-11, 2-1to 2-18, Comparative Polymer 1) had the composition shown below. Thecomposition of each polymer was analyzed by ¹H-NMR, and the Mw and Mw/Mndetermined by GPC.

Polymer 1-1

MW=8,300

Mw/Mn=1.76

Polymer 1-2

MW=8,800

Mw/Mn=1.77

Polymer 1-3

Mw=7,600

Mw/Mn=1.79

Polymer 1-4

Mw=8,600

Mw/Mn=1.93

Polymer 1-5

Mw=8,300

Mw/Mn=1.92

Polymer 1-6

Mw=8,900

Mw/Mn=1.83

Polymer 1-7

Mw=8,200

Mw/Mn=1.76

Polymer 1-8

Mw=8,400

Mw/Mn=1.88

Polymer 1-9

MW=7,800

Mw/Mn=1.85

Polymer 1-10

Mw=7,300

Mw/Mn=1.81

Polymer 1-11

Mw=8,300

Mw/Mn=1.79

Polymer 2-1

Mw=8,100

Mw/Mn=1.83

Polymer 2-2

Mw=8,300

Mw/Mn=1.89

Polymer 2-3

Mw=8,600

Mw/Mn=1.82

Polymer 2-4

Mw=8,600

Mw/Mn=1.82

Polymer 2-5

Mw=8,100

Mw/Mn=1.83

Polymer 2-6

Mw=8,300

Mw/Mn=1.94

Polymer 2-7

Mw=8,100

Mw/Mn=1.90

Polymer 2-8

Mw=8,000

Mw/Mn=1.83

Polymer 2-9

Mw=7,100

Mw/Mn=1.88

Polymer 2-10

Mw=7,600

Mw/Mn=1.81

Polymer 2-11

Mw=9,100

Mw/Mn=1.92

Polymer 2-12

Mw=8,200

Mw/Mn=1.95

Polymer 2-13

Mw=8,600

Mw/Mn=1.99

Polymer 2-14

Mw=8,300

Mw/Mn=1.82

Polymer 2-15

Mw=7,600

Mw/Mn=1.92

Polymer 2-16

Mw=7,900

Mw/Mn=1.77

Polymer 2-17

Mw=7,300

Mw/Mn=1.71

Polymer 2-18

Mw=7,200

Mw/Mn=1.74

Comparative Polymer 1

Mw=8,500

Mw/Mn=1.73

Preparation of First Resist Composition

A resist solution was prepared by dissolving each polymer (Polymers 1-1to 1-11, 2-1, Comparative Polymer 1), an acid generator (PAG1), a basegenerator (BG1 to 4), a basic compound (amine quencher), and a repellent(for rendering the resist film surface water repellent) in a solvent inaccordance with the recipe shown in Table 1, and filtering through aTeflon® filter with a pore size of 0.2 μm. The solvent contained 50 ppmof surfactant FC-4430 (3M-Sumitomo Co., Ltd.). Note that in ComparativeResist 1-3, Polymer 1-3 could not be dissolved in the solvent.

The components in Table 1 are identified below.

Photoacid Generator: PAG1

Basic Compound (Amine Quencher): Quencher 1

Base Generator: BG1 to BG4

Repellent: Repellent Polymers 1 and 2

Organic Solvent:

propylene glycol monomethyl ether acetate (PGMEA)

cyclohexanone (CyH)

propylene glycol monomethyl ether (PGME)

TABLE 1 Base Acid Basic Organic Polymer generator generator compoundRepellent solvent (pbw) (pbw) (pbw) (pbw) (pbw) (pbw) Resist 1-1 Polymer1-1 (100) — PAG1 Quencher 1 Repellent PGMEA (1,500) (14.0) (1.60)Polymer 1 CyH (500) (4.0) 1-2 Polymer 1-2 (100) — PAG1 Quencher 1Repellent PGMEA (1,500) (14.0) (1.60) Polymer 1 CyH (500) (4.0) 1-3Polymer 1-3 (100) — PAG1 Quencher 1 Repellent PGMEA (1,500) (14.0)(1.60) Polymer 1 CyH (500) (4.0) 1-4 Polymer 1-4 (100) BG1 PAG1 Quencher1 Repellent PGMEA (1,500) (2.0) (14.0) (1.60) Polymer 1 CyH (500) (4.0)1-5 Polymer 1-5 (100) — PAG1 Quencher 1 Repellent PGMEA (1,500) (14.0)(1.60) Polymer 1 CyH (500) (4.0) 1-6 Polymer 1-6 (100) BG1 — Quencher 1Repellent PGMEA (1,800) (2.0) (1.60) Polymer 1 PGME (200) (4.0) 1-7Polymer 1-7 (100) BG1 — Quencher 1 Repellent PGMEA (1,500) (2.0) (1.60)Polymer 1 CyH (500) (4.0) 1-8 Polymer 1-8 (100) BG1 — Quencher 1Repellent PGMEA (1,500) (2.0) (1.60) Polymer 1 CyH (500) (4.0) 1-9Polymer 1-9 (100) BG1 PAG1 Quencher 1 Repellent PGMEA (1,500) (2.0)(14.0) (1.60) Polymer 1 CyH (500) (4.0) 1-10 Polymer 1-10 (100) BG1 PAG1Quencher 1 Repellent PGMEA (1,500) (2.0) (14.0) (1.60) Polymer 1 CyH(500) (4.0) 1-11 Polymer 1-11 (70) BG2 PAG1 Quencher 1 Repellent PGMEA(1,500) Comparative Polymer (1.2) (14.0) (1.60) Polymer 1 CyH (500) 1(30) (4.0) 1-12 Polymer 1-3 (100) BG3 PAG1 Quencher 1 Repellent PGMEA(1,500) (2.0) (14.0) (1.60) Polymer 1 CyH (500) (4.0) 1-13 Polymer 1-3(100) BG4 PAG1 Quencher 1 Repellent PGMEA (1,500) (2.0) (14.0) (1.60)Polymer 1 CyH (500) (4.0) Comparative 1-1 Comparatve Polymer 1 — PAG1Quencher 1 Repellent PGMEA (1,500) Resist (100) (14.0) (1.60) Polymer 1CyH (500) (4.0) 1-2 Polymer 2-1 (100) — PAG1 Quencher 1 Repellent2-methyl-1-butanol (14.0) (1.60) Polymer 1 (2,100) (4.0) 1-3 Polymer 1-3(100) — PAG1 Quencher 1 Repellent 2-methyl-1-butanol (14.0) (1.60)Polymer 1 (2,100) (4.0)

Preparation of Second Resist Composition

A resist solution was prepared by dissolving each polymer (Polymers 2-1to 2-18), an acid generator, a basic compound (amine quencher), and arepellent (for rendering the resist film surface water repellent) in asolvent in accordance with the recipe shown in Table 2, and filteringthrough a Teflon® filter with a pore size of 0.2 μm. The solventcontained 50 ppm of surfactant FC-4430 (3M-Sumitomo Co., Ltd.).

TABLE 2 Acid Basic Polymer generator compound Repellent (pbw) (pbw)(pbw) (pbw) Organic solvent (pbw) Resist 2-1 Polymer 2-1 PAG1 Quencher 1Repellent Polymer 2 4-methyl-2-pentanol (3,000) (100) (14.0) (1.60)(4.0) 2-2 Polymer 2-2 PAG1 Quencher 1 Repellent Polymer 23-methyl-1-butanol (3,000) (100) (14.0) (1.60) (4.0) 2-3 Polymer 2-3PAG1 Quencher 1 Repellent Polymer 2 2-methyl-1-butanol (2,400) (100)(14.0) (1.60) (4.0) diisoamyl ether (600) 2-4 Polymer 2-4 PAG1 Quencher1 Repellent Polymer 2 isobutyl alcohol (1,200) (100) (14.0) (1.60) (4.0)4-methyl-2-pentanol (1,800) 2-5 Polymer 2-4 PAG1 Quencher 1 RepellentPolymer 2 2-methyl-1-butanol (2,100) (100) (14.0) (1.60) (4.0)1-heptanol (600) 2,6-dimethylanisole (300) 2-6 Polymer 2-4 PAG1 Quencher1 Repellent Polymer 2 2-methyl-1-butanol (2,100) (100) (14.0) (1.60)(4.0) 1-heptanol (600) 2,6-dimethylanisole (300) 2-7 Polymer 2-4 PAG1Quencher 1 Repellent Polymer 2 2-methyl-1-butanol (2,100) (100) (14.0)(1.60) (5.0) 2-pentanol (600) di-n-butyl ether (300) 2-8 Polymer 2-4PAG1 Quencher 1 Repellent Polymer 2 3-methyl-1-butanol (2,700) (100)(14.0) (1.60) (5.0) 4-allylanisole (300) 2-9 Polymer 2-4 PAG1 Quencher 1Repellent Polymer 2 2-methyl-1-butanol (2,100) (100) (14.0) (1.60) (4.0)2-hexanol (600) 2-ethylanisole (300) 2-10 Polymer 2-5 PAG1 Quencher 1Repellent Polymer 2 1-heptanol (2,400) (100) (14.0) (1.60) (4.0)di-n-hexyl ether (600) 2-11 Polymer 2-6 PAG1 Quencher 1 RepellentPolymer 2 2-methyl-1-butanol (2,700) (100) (14.0) (1.60) (4.0) n-butylphenyl ether (300) 2-12 Polymer 2-7 — Quencher 1 Repellent Polymer 22-methyl-1-butanol (2,100) (100) (1.60) (4.0) 2-heptanol (600)4-methoxytoluene (300) 2-13 Polymer 2-8 — Quencher 1 Repellent Polymer 22-methyl-1-butanol (2,400) (100) (1.60) (4.0) 4-ethylanisole (200) 2-14Polymer 2-9 PAG1 Quencher 1 Repellent Polymer 2 2-methyl-1-butanol(2,100) (100) (14.0) (1.60) (4.0) isobutyl alcohol (600) n-pentanol(300) 2-15 Polymer 2-10 PAG1 Quencher 1 Repellent Polymer 22-methyl-1-butanol (2,400) (100) (14.0) (1.60) (4.0) 4-ethylanisole(600) 2-16 Polymer 2-11 PAG1 Quencher 1 Repellent Polymer 22-methyl-1-butanol (2,700) (100) (14.0) (1.60) (4.0) 4-ethylphenetole(300) 2-17 Polymer 2-12 PAG1 Quencher 1 Repellent Polymer 22-methyl-1-butanol (2,400) (100) (14.0) (1.60) (4.0) 3,5-dimethylanisole(600) 2-18 Polymer 2-13 PAG1 Quencher 1 Repellent Polymer 22-methyl-1-butanol (2,400) (100) (14.0) (1.60) (4.0) 2,6-dimethylanisole(600) 2-19 Polymer 2-14 PAG1 Quencher 1 Repellent Polymer 22-methyl-1-butanol (2,400) (100) (14.0) (1.60) (4.0) 2,4-dimethylanisole(600) 2-20 Polymer 2-15 PAG1 Quencher 1 Repellent Polymer 22-methyl-1-butanol (3,000) (100) (14.0) (1.60) (4.0) 2-21 Polymer 2-16PAG1 Quencher 1 Repellent Polymer 2 2-methyl-1-butanol (3,000) (100)(14.0) (1.60) (4.0) 2-22 Polymer 2-17 PAG1 Quencher 1 Repellent Polymer2 2-methyl-1-butanol (3,000) (100) (14.0) (1.60) (4.0) 2-23 Polymer 2-18PAG1 Quencher 1 Repellent Polymer 2 2-methyl-1-butanol (3,000) (100)(14.0) (1.60) (4.0)

Examples and Comparative Examples Slimming of First Resist Film bySolvent

Each of the first resist compositions shown in Table 1 was coated on asilicon wafer and baked at 100° C. for 60 seconds to form a resist filmof 100 nm thick. A solvent (shown in Table 3) was statically dispensedon the resist film for 20 seconds, followed by spin drying and baking at100° C. for 60 seconds for evaporating off the solvent. The thickness ofthe resist film was measured for determining a film thickness reduction(slimming) before and after solvent dispensing. The results are shown inTable 3.

TABLE 3 Solvent Slimming (weight ratio) (nm) Resist 1-14-methyl-2-pentanol 1.5 Resist 1-1 3-methyl-1-butanol 1.6 Resist 1-12-methyl-1-butanol:diisoamyl ether = 8:2 0.6 Resist 1-1 isobutylalcohol:4-methyl-2-pentanol = 4:6 1.6 Resist 1-13-methyl-1-butanol:4-allylanisole = 9:1 0.5 Resist 1-11-heptanol:2,3,5-trimethylanisole = 9:1 0.6 Resist 1-12-methyl-1-butanol:2-pentanol:di-n-butyl 0.6 ether = 7:2:1 Resist 1-12-methyl-1-butanol:2-heptanol:4- 0.6 methoxytoluene = 7:2:1 Resist 1-12-methyl-1-butanol:2-hexanol:2- 0.9 ethylanisole = 7:2:1 Resist 1-11-heptanol:di-n-hexyl ether = 8:2 0.8 Resist 1-12-methyl-1-butanol:n-butyl phenyl ether = 9:1 0.6 Resist 1-12-methyl-1-butanol:isobutyl alcohol:n- 1.4 pentanol = 7:2:1 Resist 1-12-methyl-1-butanol:4-ethylanisole = 8:2 1.0 Resist 1-12-methyl-1-butanol:4-ethylphenetole = 9:1 0.6 Resist 1-12-methyl-1-butanol:3,5-dimethylanisole = 8:2 0.6 Resist 1-12-methyl-1-butanol:2,6-dimethylanisole = 8:2 0.5 Resist 1-12-methyl-1-butanol:2,4-dimethylanisole = 8:2 0.4 Resist 1-1 PGMEA 100Resist 1-1 CyH 100 Resist 1-1 2-methyl-1-butanol 1.5 Resist 1-22-methyl-1-butanol 1.6 Resist 1-3 2-methyl-1-butanol 2.1 Resist 1-42-methyl-1-butanol 2.5 Resist 1-5 2-methyl-1-butanol 2.1 Resist 1-62-methyl-1-butanol 2.0 Resist 1-7 2-methyl-1-butanol 2.0 Resist 1-82-methyl-1-butanol 1.8 Resist 1-8 2-methyl-1-butanol 1.6 Resist 1-102-methyl-1-butanol 1.5 Resist 1-11 2-methyl-1-butanol 1.3 Resist 1-122-methyl-1-butanol 1.9 Resist 1-13 2-methyl-1-butanol 1.9 Comparative2-methyl-1-butanol 1.8 Resist 1-1 Comparative 2-methyl-1-butanol 100Resist 1-2

It was demonstrated that Resists 1-1 to 1-13 were insoluble in thealcohol solvents and alcohol/ether mixed solvents.

Double Patterning Test I

On a substrate (silicon wafer) having an antireflective coating(ARC-29A, Nissan Chemical Industries Ltd.) of 80 nm thick, each of thefirst resist compositions shown in Table 1 was spin coated, then bakedon a hot plate at 100° C. for 60 seconds to form a resist film of 100 nmthick. Using an ArF excimer laser scanner model NSR-S610C (Nikon Corp.,NA 1.30, σ0.98/0.78, 35° cross-pole illumination, 6% halftone phaseshift mask) with azimuthally polarized illumination, the coatedsubstrate was exposed to a Y-direction 40-nm line/160-nm pitch pattern.After exposure, the resist film was baked (PEB) at 100° C. for 60seconds in Examples 1-1 to 1-35 and Comparative Examples 1-1 and 1-2 orat 80° C. for 60 seconds in Comparative Examples 1-3 and 1-4 and thendeveloped for 30 seconds with a 2.38 wt % TMAH aqueous solution,obtaining a first line-and-space pattern having a line-to-space ratio of1:3 and a line size of 40 nm.

Then the first resist pattern-bearing substrate was baked for 60 secondsat the temperature shown in Tables 4 and 5, causing the base generatormoiety to generate an amine compound.

Next, each of the second resist compositions shown in Table 2 was coatedonto the first resist pattern-bearing substrate and baked at 100° C. for60 seconds to form a resist film of 80 nm thick on the flat substrate.Using an ArF excimer laser scanner model NSR-S610C (Nikon Corp., NA1.30, σ0.98/0.78, 35° cross-pole illumination, 6% halftone phase shiftmask) with azimuthally polarized illumination, the coated substrate wasexposed to a Y-direction 40-nm line/160-nm pitch pattern which wasshifted 80 nm from the first pattern in X-direction. After exposure, thesecond resist film was baked (PEB) at 80° C. for 60 seconds in allExamples, but at 100° C. for 60 seconds in Comparative Example 1-2 andthen developed for 30 seconds with a 2.38 wt % TMAH aqueous solution,obtaining a second line-and-space pattern having a line size of 40 nm.There were formed parallel extending first pattern lines A and secondpattern lines B as illustrated in FIG. 7. The line width of the firstand second patterns was measured by a measuring SEM (S-9380, Hitachi,Ltd.). The results are also shown in Tables 4 and 5.

TABLE 4 Size of 1st Size of pattern 1st after 1st Baking 2nd patternformation Size of resist temp. resist as of 2nd 2nd composition (° C.)compostion developed pattern pattern Example 1-1 Resist 1-1 140 Resist2-1 41 nm 38 nm 40 nm 1-2 Resist 1-2 140 Resist 2-1 40 nm 40 nm 41 nm1-3 Resist 1-3 140 Resist 2-1 40 nm 37 nm 41 nm 1-4 Resist 1-4 140Resist 2-1 40 nm 36 nm 41 nm 1-5 Resist 1-5 130 Resist 2-1 40 nm 36 nm41 nm 1-6 Resist 1-6 150 Resist 2-1 40 nm 40 nm 41 nm 1-7 Resist 1-7 150Resist 2-1 40 nm 40 nm 41 nm 1-8 Resist 1-8 150 Resist 2-1 42 nm 40 nm42 nm 1-9 Resist 1-9 150 Resist 2-1 40 nm 40 nm 41 nm 1-10 Resist 1-10150 Resist 2-1 41 nm 40 nm 41 nm 1-11 Resist 1-11 150 Resist 2-1 41 nm40 nm 42 nm 1-12 Resist 1-3 140 Resist 2-2 41 nm 39 nm 41 nm 1-13 Resist1-3 140 Resist 2-3 40 nm 40 nm 41 nm 1-14 Resist 1-3 140 Resist 2-4 40nm 40 nm 41 nm 1-15 Resist 1-3 120 Resist 2-5 40 nm 40 nm 41 nm 1-16Resist 1-3 140 Resist 2-6 40 nm 42 nm 41 nm 1-17 Resist 1-3 140 Resist2-7 40 nm 42 nm 40 nm 1-18 Resist 1-3 140 Resist 2-8 40 nm 42 nm 40 nm1-19 Resist 1-3 140 Resist 2-9 40 nm 42 nm 40 nm 1-20 Resist 1-3 140Resist 2-10 40 nm 43 nm 41 nm 1-21 Resist 1-3 150 Resist 2-11 40 nm 40nm 41 nm 1-22 Resist 1-3 140 Resist 2-12 40 nm 40 nm 41 nm 1-23 Resist1-3 160 Resist 2-13 40 nm 40 nm 41 nm 1-24 Resist 1-3 140 Resist 2-14 40nm 40 nm 41 nm 1-25 Resist 1-3 130 Resist 2-15 40 nm 40 nm 41 nm 1-26Resist 1-3 140 Resist 2-16 40 nm 39 nm 41 nm 1-27 Resist 1-3 130 Resist2-17 40 nm 38 nm 41 nm 1-28 Resist 1-3 130 Resist 2-18 40 nm 39 nm 41 nm1-29 Resist 1-3 140 Resist 2-19 40 nm 40 nm 41 nm 1-30 Resist 1-3 130Resist 2-20 40 nm 39 nm 41 nm 1-31 Resist 1-3 140 Resist 2-21 41 nm 38nm 42 nm 1-32 Resist 1-12 140 Resist 2-1 41 nm 40 nm 40 nm 1-33 Resist1-13 140 Resist 2-1 40 nm 40 nm 41 nm 1-34 Resist 1-12 140 Resist 2-2241 nm 40 nm 40 nm 1-35 Resist 1-12 140 Resist 2-23 41 nm 40 nm 40 nm

TABLE 5 Size of Size of 1st 1st pattern 1st Baking 2nd pattern afterSize of resist temp. resist as formation of 2nd 2nd composition (° C.)compostion developed pattern pattern Comparative 1-1 Resist 1-3 — Resist2-1 40 nm 27 nm 41 nm Example 1-2 Resist 1-3 140 Resist 1-3 40 nmpattern 41 nm vanished 1-3 Comparative 140 Resist 2-1 40 nm 23 nm 41 nmResist 1-1 1-4 Comparative 140 Resist 2-1 40 nm pattern 40 nm Resist 1-2vanished

Double Patterning Test II

On a substrate (silicon wafer) having an antireflective coating(ARC-29A) of 80 nm thick, each of the first resist compositions shown inTable 1 was spin coated, then baked on a hot plate at 100° C. for 60seconds to form a resist film of 100 nm thick. Using an ArF excimerlaser scanner model NSR-S610C (Nikon Corp., NA 1.30, σ0.98/0.78, 20°dipole illumination, 6% halftone phase shift mask) with s-polarizedillumination, the coated substrate was exposed to a X-direction 40-nmline/80 nm pitch line-and-space pattern. After exposure, the resist filmwas baked (PEB) at 100° C. for 60 seconds in Examples 2-1 to 2-35 andComparative Examples 2-1 and 2-2 or at 80° C. for 60 seconds inComparative Examples 2-3 and 2-4 and then developed for 30 seconds witha 2.38 wt % TMAH aqueous solution, obtaining a first line-and-spacepattern having a line size of 40 nm.

Then the first resist pattern-bearing substrate was baked for 60 secondsat the temperature shown in Tables 6 and 7, causing the base generatormoiety to generate an amine compound.

Next, each of the second resist compositions shown in Table 2 was coatedonto the first resist pattern-bearing substrate and baked at 100° C. for60 seconds to form a resist film of 60 nm thick on the flat substrate.Using an ArF excimer laser scanner model NSR-S610C (Nikon Corp., NA1.30, σ0.98/0.78, 20° dipole illumination, 6% halftone phase shift mask)with s-polarized illumination, the coated substrate was exposed to aY-direction 40-nm line/80 nm pitch line-and-space pattern. Afterexposure, the second resist film was baked (PEB) at 80° C. for 60seconds in all Examples, but at 100° C. for 60 seconds in ComparativeExample 2-2 and then developed for 30 seconds with a 2.38 wt % TMAHaqueous solution, obtaining a second line-and-space pattern having aline size of 40 nm. There were formed orthogonally crossing firstpattern lines A and second pattern lines B as illustrated in FIG. 8. Theline width of the first and second patterns was measured by a measuringSEM (S-9380, Hitachi, Ltd.). The results are shown in Tables 6 and 7.

TABLE 6 Size of 1st Size of pattern 1st after 1st Baking 2nd patternformation Size of resist temp. resist as of 2nd 2nd composition (° C.)composition developed pattern pattern Example 2-1 Resist 1-1 140 Resist2-1 41 nm 37 nm 40 nm 2-2 Resist 1-2 140 Resist 2-1 40 nm 39 nm 41 nm2-3 Resist 1-3 140 Resist 2-1 40 nm 37 nm 41 nm 2-4 Resist 1-4 140Resist 2-1 41 nm 37 nm 41 nm 2-5 Resist 1-5 130 Resist 2-1 42 nm 36 nm41 nm 2-6 Resist 1-6 150 Resist 2-1 43 nm 40 nm 41 nm 2-7 Resist 1-7 130Resist 2-1 42 nm 36 nm 41 nm 2-8 Resist 1-8 150 Resist 2-1 43 nm 40 nm41 nm 2-9 Resist 1-6 150 Resist 2-1 41 nm 40 nm 41 nm 2-10 Resist 1-7130 Resist 2-1 42 nm 40 nm 41 nm 2-11 Resist 1-8 150 Resist 2-1 41 nm 40nm 41 nm 2-12 Resist 1-3 140 Resist 2-2 41 nm 40 nm 41 nm 2-13 Resist1-3 140 Resist 2-3 42 nm 40 nm 41 nm 2-14 Resist 1-3 140 Resist 2-4 41nm 40 nm 41 nm 2-15 Resist 1-3 120 Resist 2-5 42 nm 40 nm 41 nm 2-16Resist 1-3 140 Resist 2-6 42 nm 40 nm 41 nm 2-17 Resist 1-3 140 Resist2-7 40 nm 38 nm 41 nm 2-18 Resist 1-3 140 Resist 2-8 40 nm 39 nm 41 nm2-19 Resist 1-3 140 Resist 2-9 40 nm 38 nm 42 nm 2-20 Resist 1-3 140Resist 2-10 40 nm 39 nm 41 nm 2-21 Resist 1-3 150 Resist 2-11 40 nm 40nm 40 nm 2-22 Resist 1-3 140 Resist 2-12 40 nm 38 nm 41 nm 2-23 Resist1-3 160 Resist 2-13 40 nm 38 nm 41 nm 2-24 Resist 1-3 140 Resist 2-14 40nm 38 nm 41 nm 2-25 Resist 1-3 130 Resist 2-15 42 nm 39 nm 41 nm 2-26Resist 1-3 140 Resist 2-16 41 nm 38 nm 41 nm 2-27 Resist 1-3 130 Resist2-17 40 nm 39 nm 41 nm 2-28 Resist 1-3 130 Resist 2-18 41 nm 38 nm 42 nm2-29 Resist 1-3 140 Resist 2-19 43 nm 39 nm 41 nm 2-30 Resist 1-3 130Resist 2-20 42 nm 39 nm 40 nm 2-31 Resist 1-3 140 Resist 2-21 41 nm 39nm 41 nm 2-32 Resist 1-12 140 Resist 2-1 41 nm 38 nm 40 nm 2-33 Resist1-13 140 Resist 2-1 40 nm 39 nm 41 nm 2-34 Resist 1-12 140 Resist 2-2241 nm 39 nm 40 nm 2-35 Resist 1-12 140 Resist 2-23 40 nm 40 nm 41 nm

TABLE 7 Size of 1st Size of pattern 1st after 1st Baking 2nd patternformation Size of resist temp. resist as of 2nd 2nd composition (° C.)composition developed pattern pattern Comparative 2-1 Resist 1-3 —Resist 2-1 40 nm pattern 41 nm Example vanished 2-2 Resist 1-3 140Resist 1-3 40 nm pattern 41 nm vanished 2-3 Comparative 140 Resist 2-140 nm pattern 41 nm Resist 1-1 vanished 2-4 Comparative 140 Resist 2-140 nm pattern 40 nm Resist 1-2 vanished

In the patterning process of Examples 1-1 to 1-35, the formation of asecond resist pattern having lines located between lines of a firstresist pattern was observed. In the patterning process of Examples 2-1to 2-35, the formation of a second resist pattern having lines crossinglines of a first resist pattern was observed.

In Comparative Examples 1-1 and 2-1, the first resist pattern wasdissolved away in the developer during formation of the second resistpattern because of a lack of pyrolysis of the base generator by bakingafter first pattern formation.

In Comparative Examples 1-2, 1-4, 2-2 and 2-4, the first resist patternwas dissolved away upon coating of the second resist material. InComparative Examples 1-3 and 2-3, the first resist pattern was dissolvedaway during second development because the base polymer having no aminegenerator copolymerized was used in the first resist material.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention.Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

Japanese Patent Application No. 2009-181504 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A resist composition comprising a base resin, a photoacid generator,and an organic solvent, wherein the base resin is a copolymer comprisingrecurring units having lactone as an adhesive group, recurring unitshaving an acid labile group, and recurring units represented by formula(a1) or (a2) in the following general formula (1):

wherein R¹ and R² are hydrogen or methyl, R² and R⁸ are a single bond,methylene, ethylene, phenylene, phenylmethylene, phenylethylene,phenylpropylene, or —C(═O)—R¹²—, wherein R¹² is a straight, branched orcyclic C₁-C₁₀ alkylene, C₆-C₁₀ arylene, or C₂-C₁₂ alkenylene group, R³and R⁹ are hydrogen or a straight, branched or cyclic C₁-C₁₀ alkyl, orwhen R² and R⁸ are —C(═O)—R¹²—, R³ and R⁹ may bond with R¹² to form aring with the nitrogen atom to which they are attached, R⁴, R⁵ and R⁶are hydrogen or a straight, branched or cyclic C₁-C₁₀ alkyl, C₆-C₁₄aryl, or C₇-C₁₄ alkenyl group, which may contain a straight, branched orcyclic C₁-C₆ alkyl, nitro, halogen, cyano, trifluoromethyl, carbonyl,ester, lactone ring, carbonate, maleimide, amide, C₁-C₆ alkoxy, or sulfogroup, R⁴ and R⁵, R⁵ and R⁶, or R⁴ and R⁶ may bond together to form aring with the carbon atom to which they are attached, exclusive of thecase where all of R⁴, R⁵ and R⁶ are hydrogen or alkyl, R¹⁰ and R¹¹ are aC₆-C₁₄ aryl or C₇-C₁₄ aralkyl group, which may contain a straight,branched or cyclic C₁-C₆ alkyl, nitro, halogen, cyano, trifluoromethyl,C₁-C₆ alkoxy, or carbonyl group.